free-x released the game save (uuencoded) for MechAssault with the exploit similar to 007: Agent Under Fire.
So now you can also boot resigned xbe's with MechAssault.

Check it out on xboxhacker.net BBS.
I decode the uu-txt in linux (for some reason it didn't work with my win32 uudecode (probably 'cause of the base64)), you can download it here (no copyrighted code or libs are used - this file is 100% legal)