It's an interesting idea, but in short, no. Nobody has developed the hardware to convert any of the Xbox's outputs to the iPad's. I think it could be done though.
If you just wanted to see it work (not really for gaming)
Amazing Iceman had it right, you could buy a capture device (I would not recommend EasyCap) and view the game on your computer and then use a VNC client on the iPad to view the computer's screen.
j3yq was right though, it would have severe latency (maybe not lag), any game would be almost unplayable if you did it this way.
I doubt it. I'm already streaming high resolution video to my iPad using AirVideo. A computer that is powerful enough could stream a live video feed from an XBox 360. No lags.
It wouldn't necessarily have anything to do with the computer's power, more so the router's speed. I've not used AirVideo, but I'm 99% sure that it doesn't do a 100% live stream of the video. I think AirVideo buffers the video first (like YouTube).