Shoutbox

If you've got 512MB of PC3200 (400MHz) DDR buying another 512MB of PC3200 won't increase the speed (unless Dual Channel) just enable you to do more.

IMO 256MB is the absolute minimum for Windoes XP which makes Windows XP 64bit 512MB minimum (since 64bit is twice the data chunk size of 32bit).

If you play games (casual gamer) 512MB is fine, if you're hardcore then 1GB is the minimum you should use.

CAD/CGI & even heavy Video Editing also 1GB is the minimum you should use, while 2GB will be better.

A server really doesn't make sense with les than 2GB of RAM as they tend to do a lot of tasks simultaneously.

EDIT:  once your RAM is full it will use your Page File (Virtual Memory) which is vastly slower than RAM and in that way more RAM will seem faster.