There is a processor GPU on the card that unloads the graphics tasks from the CPU. It communicates with CPU through the lanes on the motherboard. The CPU speed matters in itself since it has to have speed to handle the information (data) from the GPU. Hence we have the term bottleneck when the CPU is not fast enough to handle the data from the GPU to its full potential.
Great, so you think I should be ok with this:
p7p55d pro mobo(Asus) I5-750
EVGA GeForce GTS 250 512MB DDR3 PCIe DVI/HDMI/VGA
8 gig ram