I try to go with a gig these days. Although if your doing anything real advanced like gaming or webserving, 512 is plenty.
The extra 512 just allows for a bit more power. I have (2) 256 pc2700's im looking to sell, if anyone is interested.
But yeah, 2 gig's would be ideal for gaming and more advanced computing.
My mian system is as follows:
Amd Athlon XP 3200+ (2.2ghz)
1 gig of pc3200 ram
160 gig 7.2k rpm
DVD+RW/CD-RW
CD rom
And a Nvidia GeForce 5700
It ran the prey demo, great. So, I don't think im going to upgrade for a long while. Lol.