71.89 are not the best of drivers. I have a 6600GT and played manhunt with no problems. Try using 76.45, or better yet 77.30. You are going to have to try and find out which one works best. Refer to the first thread on the video section for the drivers. And try to decrease the maximum number of frames drawn thing to 1 or 2, though they suggest that for racing games most of the time.