So what did u end up to do, than?
I knew you could do it through the registry editor but I couldn't remember how exactly. I looked it up and it took awhile but I found out how to do it. It was pretty easy really. This is how you do it:
1) Click Start button > Run.
2) At the prompt type: REGEDIT. The registry editor will open.
3) Click the "+" next to HKEY_LOCAL_MACHINE.
4) Click the "+" next to SOFTWARE.
5) Click the "+" next to ACTIVISION.
6) Right-click on the CALL OF DUTY folder and select Delete.
7) Close the registry editor.
Once the registry keys are removed you have to remove the game files from your hard drive. Then re-install and it should be as if the patch never happened