As you have a relatively powerful CPU there, I'd look and see if your GPU supports CUDA or OpenCL. A GPU miner (like one of the 4 *.exe files you already have downloaded in the RPC package) can achieve fairly high khash/s figures with less strain on your CPU. The GPU on my laptop, for instance, supports CUDA although it required a driver update before it would work, and it's just as fast as my two CPU cores combined running at max speed. This is with a relatively weak GPU, even by laptop standards.
I have a nVidia GeForce 6150SE which, according to the GPU Caps viewer does not run OpenCL or CUDA, only OpenGL. That after I updated to the latest driver from nVidia's website.