well ive noticed that bf2 can suck up to 840 megs of ram on my system, which has 2 gigs, l would not like to run bf2 with 512 megs, 1 gig would be alot better, saying that though, the single most important part of a pc for games is its video card, so you ve asked a question like, ''does my car need a motor or wheels more'' half life on my pc can use up to 508 megs of ram, l would upgrade the video card to the best you can afford, then save for the 1 gig mark in ram, that way you will get smooth gaming im most games for alot longer.......
Fundamently its mo bo, cpu, vid card, ram, hd, sound card, usually in that order by gamers...