I think you should just buy an HD 4670 and that ram that other person mentioned. That will get you up to a pretty good gamer spec for the next few years at least. That card is excellent I use it in my HTPC because AMD cards can output sound via HDMI (dongle) and it works really well. Its got 2x the shader power and 3x the texturing of an Xbox 360 so it should do you just fine.
This should run you up to about $120 incl shipping for both ram and the graphics card. If you go any higher you'll need to buy:
- A new CPU
- A new PSU
- perhaps even a new motherboard.
K.I.S.S. 
Tease.







