Affinity Mask?

[badaboom]

Hello,I've finally bought the English version of CoD after buying the Russian version when the game first arrived.Ive been away for along time but The English version is stuttering Badly.

I seem to remember a tweak to add Affinity Mask to run on all CPU cores,Is this tweak still valid?THX
Quad @4.1GHz
8GIg DDR2 Ram
GTX580