2 Main problems that may help.

Nvidia nforce_winvista64_15.17_international drivers cause frezzing under COD4.
Nvidia nforce_winvista64_9.64_english_whql drivers work 100% For My Setup.


BFG 9800GX2 174.74 Video drivers work 100%
BFG 9800GX2 17x.XX Video drivers cause frezzing or driver has stopped working & has recovered.

Hope this helps maybe a few people....