Well enough money can make anything happen. But the real issue is the fact that XBox is a closed system. Even if you had the ability to create an XBox CD you couldn't run it on your own XBox without breaking the law. You probably wouldn't get sued for it, but Conitec sure would for making the engine.

It isn't likely that Microsoft is going to open up their console any time soon. This is a “big budget” market, and you need serious money to play in it. You might want to look at their “Live Arcade” option however.