Sorry that was wrong it's Dual Core support that needs turning off even if you have Dual core.
i nkow cod 5 doesnt seem to like scaling on my quad sli setup, but it does improve the fps overall, just gets more stuttering. Not sure what mal30 is on about as i wasnt expecting you to be changing that setting as well. have you turned on the support for dual video cards in cod 4? Im pretty sure it has the option.