You've not many choices with $360 left. You need an OS ($100), an HD ($50 min), memory ($85 for 2x2GB) leaving $125 for cpu and gpu. Which would cover an i3 530 and using onboard graphics. That would do for all except gaming.
If you don't need an OS, you could use the now remaining $110 to buy an HD 4850 or GTS 250 which will provide "Exceptional 1680x1050 performance in most games, (adequate) 1920x1200 in most games with lowered detail."