I'm almost certain you cant. The xbox wasn't designed with a video input, just like most PC video cards aren't. You can't just tell the system to do it. Since they'd never want you to do this, i'm sure you cant, just like you cant burn DVDs to the xbox, since it doesn't have a dvdr or cdr even though so many people for some reason think you should be able to do that.
oh and btw: you also cant emulate the ps2 or cube on an xbox.