Forget it with that rig, you won't get any good performance. Really not. You need:
- 4 core CPU with 3.0+ ghz (an i5 would be good)
- 8GB RAM
- 2GB VRAM Video Card, preferably Nvidia
- SSD - Hard Drive if possible.
I guess it is time for a new computer... I don't know your budget, but as I said, with your rig, CoD won't run on a satisfying level. You can try to install the team fusion patches, they will improve performance a bit:
http://theairtacticalassaultgroup.co...t=5058&p=52711
Also, I recommend asking questions on the ATAG-Forum linked above. This place here is more or less dead.