My computer is an AMD64 2800+ running at stock 1.8GHz, with 1 gig of ram and a super-old video card, an nVidia 4200 from 2001. When I play games on Standard or larger, the game is unacceptably slow in the later ages. What could I upgrade to improve performance? Would getting an extra gig of ram help, or should I just save up for a new computer with a current cpu and video card?

<removed my useless info>

sorry ^_^

That won't make any difference. Athlon 64 2800+ is a single-core processor

.... really ... I guess you are right.
hmmm.. mine is a amd64 3000+ and I was told to download that (for a different game, different forum) It did seem to make something of a difference. But that must have been my imagination playing tricks on me.

civ 4 uses memory, then some memory, then more memory and then some (graphics) memory - you could probably run it on a 386 with 4GB or RAM an a good graphics card :evil:
(not really - but any of todays machines has enough processor capacity to run it - if it runs xp it runs civ).
If you want to upgrade buy memory, lots of it, then your graphics card only has little physical memory - so that would be the next one to upgrade ;) I would recommend: buy some memory you will notice a performance boost - the good thing about memory is: its easy to port to your new machine once you buy it eventually :p and its pretty cheap...

That sounds exactly like the RAM bottleneck I used to have. Monitor your RAM usage, and if it approaches 1 GB (or if the pagefile goes over if you're running XP), then you need more memory. The video card should be adequate - an nvidia MX440, more or less the budget equivalent of yours, is fine - and, if your processor is equivalent to a Pentium 4 2.8 GHz as AMD says it is, you should only be getting about 30-second delays around 1850 on Huge (provided you have enough RAM).

and its pretty cheap...
Not so cheap when you're using DDR

an nvidia MX440, more or less the budget equivalent of yours, is fine
MX cards aren't fine if you have BTS. Leaderheads won't work properly since MX cards don't have pixel shaders

if your processor is equivalent to a Pentium 4 2.8 GHz as AMD says it is
AMD stopped using PR ratings for Athlon 64 processors. A64 2800+ is roughly equivalent to P4 3.2ghz

If your video card is the 64 mb card it looks like it is from looking on google, then that is definitely your bottleneck. Once you get something in the 256mb or more range it should run much better.

Not so cheap when you're using DDRI dont know where you've been shopping but you can get 2gb of DDR2 800 for $36.00 these days:

http://www.newegg.com/Product/Product.aspx?Item=N82E16820145590 (http://www.newegg.com/Product/Product.aspx?Item=N82E16820145590)

DDR2 does not equal DDR