CPU usage at 100% is completely normal, especially considering your CPU is a HT dual-core. I wouldn't recommend overclocking you CPU (nor you VGA), since it's a notebook. Mobile platforms have limited thermal envelope, and are built with strict power limitations, pushing them above specifications will most certainly cause you problems. If you aren't getting enough frames, look for software optimizations first, then if it's not enough, consider pushing the hardware.
Look on MW3 forums for graphical configurations that will improve your performance. In my experience, software tuning is much more likely to have a notable impact on performance than overclocking.