CPU: E8400
RAM: 2GB 800MHz on XP 32, 4GB 800MHz on Vista 64
Motherboard: Possibly a X38/48, P35/45
GFX CARD: HD 4850, or 8800GT/9600GT if the HD 4850 is a bit much
A simple 320GB drive, or less. Go Velociraptor if possible.
DVD+RW: Personally I'll use anything on this one, just buy top rated ones
PSU: Corsair 520w, 650w+ is OVERKILL, unless of course, you go Crossfire/SLI then it may be needed.
This should last you a very long time, you will be able max most of the games now and the upcoming ones.
I advise getting a new monitor though, I mean 19" for HD 4850 will be a waste IMO, 8800GT/9600GT will be able to handle that for you, which will cost you cheaper.