It is an issue with the cod:bo itself. A bad port i guess.
The cod:bo uses CPU instead of the GPU for calculations so if you don't have a good CPU, it would lag. To solve it (or at least reduce some lagging), find the cfg files and enable the options to use "multi-threading".
I can't recall the exact cfg file name and configurations to enable but just Google. Most people had problems with this game even on a geforce gtx 580! and the cfg file tweaking helps a bit (it solved the issue for me at least).
Hope this helps.
[Edited by Gladiat0r, 7/1/2011 9:02:31 AM]
hmmm.. cfg modifications? i'll try that, but cod:bo didn't lag when i was using gtx 9600 (and same phemon X2 555 cpu)
Have you tried reinstalling DirectX 9 for XP and Update the DX11 on 7?
Also check that you haven't set anything previously in the Nvidia control panel to let the CPU use Physx and CUDA elements, it should be used onboard.
Failing that it could be the GPU is experiencing problems like Artefacts or hardware degredation, if its still under warranty get it changed, ASUS has to honour that warranty.
do you have direct link to have most update dx11? because i thought dx11 update bundle from cod: do is enough..
thank you