Do you also need an OS and a monitor?

Maybe something like these

http://www.maximumpc.com/article/fea...y_crysis_40fps
http://www.tomshardware.com/forum/26...-budget-gaming
http://www.tomshardware.com/reviews/...lock,2113.html
http://budget-pc-build-2009.blogspot...-nov-2009.html

Lots of guides on the net to follow. Just modify where you think you need to (e.g., less $ on a video card to gain more RAM or a faster CPU).

You probably want at least 4Gigs of RAM if not more (depending on your OS).