C#: Perform Operations on GPU, not CPU (Calculate Pi)

It's a very new technology, but you might investigate CUDA. Since your question is tagged with C#, here is a .Net wrapper.

As a bonus, it appears that your 8800 GTX supports CUDA.

You might want to look at this question

You're probably looking for Accelerator, but if you are interested in game development in general I'll suggest you take a look at XNA

Another option that hasn't been mentioned for GPU calculation from C# is Brahma.

Brahma provides a LINQ-based abstraction for GPU calculations - it's basically LINQ to GPU. It works over OpenGL and DirectX without extra libraries (but requires SM3). Some of the samples are fairly amazing.