GPU rendering, AMD Radeon 7950, Windows 7, Blender 2.66a

How do I get blender to use my gpu for rendering? my gpu should be able to accommodate tonnes more vertices when I sculpt, and rendering with gpu, it seems to want to use my cpu (Intel i7) instead when rendering. I should be able to hear my gpu roar into action when doing rendering but nothing.

GPU rendering only works with CUDA compatible graphics cards, so NVidia only.