playing xbox on my comp

Ok my comp comes with the red white and yellow plugs (the audio and video ones you know) and well my xbox has those same cords... so shouldnt i be able to hook my xbox to my comp and have it come up on my screen? well i plugged it in and i couldnt figure out how to get it to come up... any help would be great... or am i just way out in left field on a ground out to second?