I've been recently studying Windows 7 64 bit and it itself needs 2GB RAM for a smooth run without any problems, so that leaves 1GB RAM for games and stuff, which is pretty low imo.
On the other hand you don't need to have 6543246546GB of RAM, I think the optimum for today's era is 4GB, I myself have W7 64, 4 Gigs of RAM and I have absolutely no problems at all.
With Phenom X4 965, 4Gigs RAM and some decent GPU you should be perfectly fine. I myself have GTX470 and I can max out every game there is for over a year. Remember that by maxing out I don't mean 1280x1024 resolution, but 1920x1200 and at least 4xAA.