K -- then installation is simple.
1-Rip the game to your Xbox hard drive (I usually keep my games in F:\Games). You can use a program called DVD2Xbox to rip the disc to the hard drive directly in your Xbox, or you can extract an ISO and transfer the game to the hard drive.
2-Once the game is somewhere on your hard drive, extract the contents of the mod to a temporary folder.
3-FTP the contents of the mod directly to wherever MUA is installed on your Xbox hard drive. So if MUA is in F:\Games\Marvel Ultimate Alliance, transfer it there. Default.xbe should replace the original default.xbe, then then the folders fall into place after that.
Hopefully that's clear.