i would recommend this for that price range NEW XFX GeForce 8800GT 256MB DDR3 PCI-E+ Call Of Duty 4 - eBay (item 220250080990 end time Jul-01-08 14:08:14 PDT)
8800GT 256mb..... but your power supply also needs upgrading
im guessing the PSU is the one that came with the case...? its doubtful it even has a 6pin connection for pci
this card requires a minimum of about 24A on the 12v rail ....but its graphically amazing
if you want a card that will run on current H/W then this will do... NVIDIA GeForce 8600GT 8600 512MB SLI PCI-E Video Card - eBay (item 110266159732 end time Jul-01-08 17:07:37 PDT)
this requires no external power ...but its a poor card (compared to the 8800) graphically this card is pleasing on the eyes as long as you don't move...lol
it delivers a bit of chop on modern games....
it all depends how involved you want to get.....