After reading lots of similar crash reports, i'll throw my two cents in. In a rusty english, sorry... 
I stopped playing Civ4 for a couple weeks having too much crashes, waiting for the patch. Now I've reinstalled the game and patched it, but the situation hasn't changed at all. My issues are the common freeze issues : PC locks up mostly in the later game (almost never had a crash in the first turns, apart from one particular case, that i'll explain to you later), during or immediatly after some heavy memory eaters moments. I'll try to be exhaustive, I've seen many people with issues like mine, maybe I'll be of little help to someone.
I tested it in many ways, and i can tell that these moments can usually be :
- Wonder movies : it never happens until mid-later in game, sometimes when a wonder movie loads up it plays for just a couple frames then it locks up, the sound goes crazy for some seconds, then the screen goes to blue or rainbow. Then, sometimes, the game screen comes back up (often quite unaligned), but in a freeze status. The mouse will often still move, but everithing else will not. A couple times i managed to switch to desktop with a CTRL ALT CANC, terminating civ4 manually : I often have some video card error messages, and i need anyway to reboot the system, 'cause it's more or less sluggish, about in the same way as it would be if i wouldn't been able to close civ (100% CPU usage and so on).
- Diplomatic screens : same issues as with the wonder movies, but less often, and it seems to happen only when in the previuos turn i made something "big"... (see next point)
- Maps Exchange : this usually don't locks up the system by itself, but it seems to stress it quite a lot, and if immediatly later i have a wonder movie or a diplomatic screen, chances of locks up are much greater. The Map itself, then, seems to be quite heavy for the system, the more i have revelead, the more locks up there will be (and not, it is not just a coincidence of the later stages of the game, see the next point)
- World Editor : opening (and closing) the editor takes a lot of time, 'cause it loads the whole map status mostly. Even doing this in the first game turn, can create a crash. In my experience, when crashes comes from the Editor, the crash (while still being most of the times an hard crash that force you to reboot), it usually don't show blue screens, it just freeze (often the background music will still play, at least until the end of the track that was playing at the crash moment).
- Permanent Alliances : this will be a major stress for your memory, and if you already have random crashes like the ones i explained before, this one will almost everytime kill your game and machine. Maybe if you force it in the first turns, when the two civs have few units and just a little part of the map revelead it will not crash so easily (this is the only thing i've not tested).
Now, IMHO, seeing this happening on different systems, with different specs, video and soundcard, i'm quite sure it is a memory leak problem in the game itself, and it is not related to a specific driver or config. It happens usually when the game encounters the heaviest needs, both video and sound ones. I've seen people experiencing less crashes when downgrading to previuos drivers, others when taking the AGP from 8X to 4X or even less, but no fix seems to work for everyone, or for everyone in the same way.
I tried myself many of these possible solutions, and i came to an answer that seems quite idiot, but works for me : everything, just everything, that will free memory, that will reduce someway the number of "events" going on in the background, will probably help more or less the stability of your game (this is quite obvious, but in this case is worth much more than the usual). Even the simple trick of manually closing every app in background (AV's, control panels, connection itself, Explorer and so on) will lower machine stress and so the crashes (and btw, it will help perfomances). This is why someone noticed better results with other tricks, like the AGP speed (reducing it is less stressing for the system, but sometimes perfomance will be worse), and probably why sometimes previous video drivers are better, mostly when previous drivers are less invasive and memory eaters (example : the latest 5.1x ATI drivers seems to me far WORSE in memory managing than the older 4.1x).
At this point, every system is unique, I have no results by downgrading drivers or AGP speed, but just playing the game only on a fresh boot and after closing every unneeded app from the task manager, make my games quite playable even in 2200. I just have to pay attention when i exchange maps, or when i'll put satellites in orbit, or before a wonder movie when i know the game has done many other stressing things in the same or previous turn. Sometimes it still crash, but less often, and, that way, i've always a safe save just before the hot spot.
Anyway, heavy issues like this one seems to be quite common nowadays in many recent games. X3 Reunion, to make an example, because of a rushed publication, went out with a huge memory issue, that still is causing very similar issues to many people (with almost identical - and unluckily less effectively - workarounds). I don't know if these similar happenings are caused by many developers going too far for today's medium pc's needs, but one thing's for sure : there's far less technical (and customer) care in recent software gaming products than how it should be. And I'm very disappointed in still seeing patches fixing minor and collateral issues leaving the customers a product often just broken. I buy a gae to have fun in my spare time, not to go crazy in finding homemade fixes for it's bugs, or to play praying every turn to don't have to reboot, until the day a harsh reboot will make some damages to my hard earned PC.
I stopped playing Civ4 for a couple weeks having too much crashes, waiting for the patch. Now I've reinstalled the game and patched it, but the situation hasn't changed at all. My issues are the common freeze issues : PC locks up mostly in the later game (almost never had a crash in the first turns, apart from one particular case, that i'll explain to you later), during or immediatly after some heavy memory eaters moments. I'll try to be exhaustive, I've seen many people with issues like mine, maybe I'll be of little help to someone.
I tested it in many ways, and i can tell that these moments can usually be :
- Wonder movies : it never happens until mid-later in game, sometimes when a wonder movie loads up it plays for just a couple frames then it locks up, the sound goes crazy for some seconds, then the screen goes to blue or rainbow. Then, sometimes, the game screen comes back up (often quite unaligned), but in a freeze status. The mouse will often still move, but everithing else will not. A couple times i managed to switch to desktop with a CTRL ALT CANC, terminating civ4 manually : I often have some video card error messages, and i need anyway to reboot the system, 'cause it's more or less sluggish, about in the same way as it would be if i wouldn't been able to close civ (100% CPU usage and so on).
- Diplomatic screens : same issues as with the wonder movies, but less often, and it seems to happen only when in the previuos turn i made something "big"... (see next point)
- Maps Exchange : this usually don't locks up the system by itself, but it seems to stress it quite a lot, and if immediatly later i have a wonder movie or a diplomatic screen, chances of locks up are much greater. The Map itself, then, seems to be quite heavy for the system, the more i have revelead, the more locks up there will be (and not, it is not just a coincidence of the later stages of the game, see the next point)
- World Editor : opening (and closing) the editor takes a lot of time, 'cause it loads the whole map status mostly. Even doing this in the first game turn, can create a crash. In my experience, when crashes comes from the Editor, the crash (while still being most of the times an hard crash that force you to reboot), it usually don't show blue screens, it just freeze (often the background music will still play, at least until the end of the track that was playing at the crash moment).
- Permanent Alliances : this will be a major stress for your memory, and if you already have random crashes like the ones i explained before, this one will almost everytime kill your game and machine. Maybe if you force it in the first turns, when the two civs have few units and just a little part of the map revelead it will not crash so easily (this is the only thing i've not tested).
Now, IMHO, seeing this happening on different systems, with different specs, video and soundcard, i'm quite sure it is a memory leak problem in the game itself, and it is not related to a specific driver or config. It happens usually when the game encounters the heaviest needs, both video and sound ones. I've seen people experiencing less crashes when downgrading to previuos drivers, others when taking the AGP from 8X to 4X or even less, but no fix seems to work for everyone, or for everyone in the same way.
I tried myself many of these possible solutions, and i came to an answer that seems quite idiot, but works for me : everything, just everything, that will free memory, that will reduce someway the number of "events" going on in the background, will probably help more or less the stability of your game (this is quite obvious, but in this case is worth much more than the usual). Even the simple trick of manually closing every app in background (AV's, control panels, connection itself, Explorer and so on) will lower machine stress and so the crashes (and btw, it will help perfomances). This is why someone noticed better results with other tricks, like the AGP speed (reducing it is less stressing for the system, but sometimes perfomance will be worse), and probably why sometimes previous video drivers are better, mostly when previous drivers are less invasive and memory eaters (example : the latest 5.1x ATI drivers seems to me far WORSE in memory managing than the older 4.1x).
At this point, every system is unique, I have no results by downgrading drivers or AGP speed, but just playing the game only on a fresh boot and after closing every unneeded app from the task manager, make my games quite playable even in 2200. I just have to pay attention when i exchange maps, or when i'll put satellites in orbit, or before a wonder movie when i know the game has done many other stressing things in the same or previous turn. Sometimes it still crash, but less often, and, that way, i've always a safe save just before the hot spot.
Anyway, heavy issues like this one seems to be quite common nowadays in many recent games. X3 Reunion, to make an example, because of a rushed publication, went out with a huge memory issue, that still is causing very similar issues to many people (with almost identical - and unluckily less effectively - workarounds). I don't know if these similar happenings are caused by many developers going too far for today's medium pc's needs, but one thing's for sure : there's far less technical (and customer) care in recent software gaming products than how it should be. And I'm very disappointed in still seeing patches fixing minor and collateral issues leaving the customers a product often just broken. I buy a gae to have fun in my spare time, not to go crazy in finding homemade fixes for it's bugs, or to play praying every turn to don't have to reboot, until the day a harsh reboot will make some damages to my hard earned PC.
