The first release of MAME-X for Xbox has been released today. Check it out here: http://kustom.demented.org/~jiggaligga/mame-x/

And check it out in this thread at Xboxhacker.net: http://216.127.72.24/cgi-bin/ikonboard/ikonboard.cgi?s=3d15beca6d28ffff;act=ST; f=2;t=50

The official site has moved to http://xbox.mame.net