Check to make sure you download the right client then. The are ones for single core CPUs, multicore CPUs, Nvidia GPUs, ATI GPUs, plus a load of beta clients.
My 8800GTX will munch through an average sized work unit in about 2-3 hours. My single core client running on a quad core CPU will do a smaller work unit in about 5-10 hours. Most of my points are from the GPU.