$1500 is a massive budget for a "budget" computer. I built an entirely new tower and manged to throw in a keyboard for $640. Just scrounge your old DVD drive and hard drives to save a nice chunk of change.

-AMD Phenom II X4 965 BE
-ASRock G870 motherboard with Crossfire support
-HD5770
-Antec 300 case


As for your current build, well, nothing short of an HD5870 or GeForce GTX480 would do justice. Also, if you are getting an i7 950, you want 6GB of RAM to take advantage of the triple channel that the motherboard WILL have. Oh, and X58 motherboards ain't cheap either.