I wouldn't spend that kind of money now with cheaper dx10 cards coming out early next year. X1950 PRO>7900GS but a bit more expensive. 7900GS can be had for as little as $150 and should be fine until sometime next year. All depends on what quality settings you want and what res you want to play at. 7900GS is cooler and reqs less power. I'd go with that.
Refer to the Guide in the Video Card section, and search there also. Wrong forum btw.