video head transplant

AtomBomb

So I'd like to take a crappy youtube video and replace the head of the person in it with the head of someone else. It's okay if it's cheesy. I'd just be using a still shot of the persons face, but the original person in the youtube video does move around a bit, so I'd have to follow him around. Is there a quick and dirty way to do this? I even thought of using fraps and moving the head in real time, but I can't think of a way to attach it to my mouse pointer.

If that's not possible, I seem to remember some website where you could make stupid videos with headshots. Anyone know where I can find it?

This is for a going away party thing. It's tomorrow, and the people that brought it to me don't really understand how involved it could get.