Huge Celtics slowdown problem

I'm in desperate need of help because this problem quite frankly is driving me nuts. I am playing a Celtics season and now i've reached the Eastern finals. For the past two games inexplicably the frame rates drop significantly up to the point that it's unplayble. The drop doesn't start from the beginning of the game. Usually it's around the end of the 1st quarter and it lasts most of the times until the end of the game. There have been times when the frame rates returned to normal but they have been sparse and even then, it doesn't last long as after a while the frame rate drop yet again. After experimenting, i have come to the conclusion that this is something that happens only when i play the Celtics. No other team has any issues. I haven't made any change to my system or my 08 installation. It run just fine up until the last games of the Eastern Semifinals. Since then it's been impossible. As i stated, every other team runs smoothly both in exhibition and in season. I'm at a loss here. I haven't added/changed anything. This happened completely out of the blue. All my other applications run fine. Help please !

XP 32bit, 3.4 Ghz, 8800 GTS, 169.25 Forceware.