The two biggest power draws in a PC are the CPU and the GPU if any. If you'll be using the IGP, then any of the good 300W+ units will be fine. If you'll be using a single GPU, then you'll probably need a good 450W or so. This greatly depends on the GPU. If you'll be running two or more GPUs then either the new 650W gold units, or a 750W or more will be needed. A case uses no power (fans some, but not much.) and a motherboard is around 10W last I looked. This is nothing compared to the 125W CPUs that are out there.