Currently UnleashX only plays WMA files, either from the Xbox's soundtrack feature or a directory of your choice. In the Tools section on xbox-scene, there's a utility to copy wma's straight to your xbox without having to burn them to a CD before. You'll have to convert your mp3's to wma's before though.. you can use dbPowerAmp (at
www.dbpoweramp.com), it's a free music converter.