I'm having similar problems as others here, my system is doing a complete hardlock sporadically after I load a saved game, enter & exit the world builder, and/or load/reload scenarios. Mouse freezes, sound stops, unable to turn numlock on/off: basically nothing short of pressing reset will fix.
As an interesting side note, I have experienced this hardlocking with one other game only, World of Warcraft which will do the exact same hardlock if I minimize and restore the window too many times (again infrequently).
System Specs:
Asus P4S800D-E /w 1008 BIOS rev.
Pentium 4 2.8e /w all standard timings, no OC
Antec NeoPower 480w ATX PS
2x 512 MB Corsair PC3200 unbuffered DDR 2.5 CAS /w standard timings in dual channel mode
Leadtek GeForce 6800GT AGP /w 81.85 drivers and standard timings, no OC
Sound Blaster Audigy ZS 2 Gamer /w 1.84.55 drivers
2x 36.7GB WD Raptor SATA in RAID 0, setup as primary partition (C) max size, 32k cluster NTFS FAT
300GB Seagate SATA, setup as storage drive (D), max size NTFS FAT
Sony DRU 800A DVD+/-RW
Logitech MX700 Combo
Dell 2005FPW DVI connected
System Setup:
Windows XP Pro w/ SP2 and all latest windowsupdates
DirectX 9.0c
AVG AntiVirus (latest)
Sygate Personal Firewall 5.6
SiS AGP(GART) Driver 1.21
SiS RAID driver package 3.04c
Custom Windows swap space: min=1024MB, max=2048MB
System Restore disabled
Windows Firewall disabled
Automcatic Windows Update: manual startup
System Health:
Defragment drives weekly
Spyware scan (ad-aware & spybot) weekly
Basically this system is in tip top shape and is constantly cared for. I usually reformat every 6 months, and I'm about half way through my format cycle. I generally run all my games in 1680x1050 with 2x AA and get pretty acceptable frame rates. The crashing is making this game very difficult to play (I'm not a save every turn player, but I do like to try different setups a lot) and I'm a little nervous as it seems there are a lot of people with very different system configs who experience similar hardlocking.
Civ4 seems like such an incredible game, and definitely in the direction I've been wanting it to take. I just wish I could actually play the damn thing where I don't have to play ironman style to avoid crashing.