You need a mod chip installed to run unsigned code.
As for right now you can run
Linux
win95
win98
win2000
There are also drivers so you can use a keyboard and mouse. You will need to modify a joy stick cable to use them. and no you can not use a keyboard and mouse with a game -yet
Check out:
http://www.xboxhacker.net/
From here you can find links to all the other info.
Remember this site if for modding and using code. Not intended for pirated games.