The Witcher 2 seems to be heavily CPU bound, with very frequent drops running on my system even at minimum settings, albeit a higher average than at high settings. Your processor is a few years old now, and the older Core 2 architecture just doesn't keep up with modern processors, even at significantly lower clock speeds. It's probably in your interest to start saving up for a new system one of these days... I'm sure your computer can still handle most games as-is fairly well, but give it another year and you're definitely going to start feeling its age.