I agree with cleeve. My friend was having similar problems with his system (X1800XT, 2.2GHz Athlon X2, 2 gigs of ram). He was getting strange, erratic, low fps readings and then after waiting for a few hours and getting back on the server it was back to normal. It was also like 1AM when he got better frames, but usually he was at 60+ with highest settings (1680 X 1050).