That looks like a solid build to me. I'd say stay with the 4gigs if your going with Vista. That way you can have some stuff open and still game with ease. Vista uses roughly 800megs of ram in itself. A higher end game can easily eat up 1gig then if your running gadgets etc your well over 2 gigs. Unless you don't mind exiting out of everything when you want to game go with 4 gigs for Vista.
And as everyone else said get the 8800GTS at minimum. 320meg is fine for 1280X1024 and lower anything above go with the 640meg edition.
^you too gplpark, okay guys were getitng off topic..free, could you recommend a PSU for me? no less than 650 watts...hmm... I might be ablet o chip in an extra 300 dollars and get that gtx...