you could prob get a mid range Core2 duo E7300 or E7400 with an 9800GTX+ easilly for $1000
if i was to recommend something it would be
Asus P5Q or thereabouts
E7300 to E8400
9800GTX+
2GB+ ram
You could use your existing card for that PC if you wanted to...
Stear clear of AMD and ATI, because atm the bang for buck is pretty minimal
im sure a ton of people will disagree with me tho...