Take a look at at AT Buyers Guide series. The "Budget" system with a few small upgrades would seem to fit your price range. In general, there's no way you're gonna get "great graphics" on a $650 budget. Having said all that, my suggestion would be to save for a few more weeks and go for this:
CPU - AMD AthlonXP 2500+ (Barton) RETAIL - $80
MB - ABit NF7-S (w/ sound + ethernet) - $85
Memory - Corsair VS 1x512MB PC3200 - $84
Video Card #1 - ATI Radeon 9600Pro - $125
Video Card #2 - ATI Radeon 9600XT - $150
Video Card #3 - ATI Radeon 9800Pro - $205
Hard Drive - 80GB WD800JB 7200/8MB - $69
Monitor #1 - NEC AS900 19" - $175
Monitor #2 - Samsung 750S 17" - $114
CDRW - Sony 52x32x52 - $25
Case/PS - Anything with 300W ATX - $50
Misc - keyboard, mouse, etc. - $50
The only way to get this system even close to your budget, is to go with the 17" monitor and the 9600 Pro graphics card ($682). Not a bad system at all, but I'd try and dig around for another ~$150 and get the bigger screen and better video.