Ok, first off, there is no loop region, you can ONLY include the portion of the song that is supposed to loop. No intro, bro.
Second, convert it into a .ogg file (Ogg Vorbis Audio file) and make sure it is under 1mb in size. Anything more and the music list ignores it.
Third, to add it to music, follow the steps in the Installing Music tutorial in the Music topic.
Lemme know if that doesnt work.