I'm not sure what your trying to do in the question.
If its to copy or amend your soundtracks that you have put on your xbox, then search Xbox-scene for XBOX Soundtrack Editor v0.97
this will allow you to copy the WMA files from your soundtrack to your PC, which you should be able to play straight off or can convert to MP3.
If you are trying to rip the audio from say a game like Vice City and turn it into MP3's then I can only think or extracting the ISO and seeing what is inside. To be honest I have never looked!