Open the 'data.jar' file with your favorite archiver (such as winzip or winrar). The music is in Ogg/Vorbis format in the 'music' subfolder inside that .jar file.
Thanks! I thought the team would be more present with the launch of their baby and that they would reply much faster to such fan request. Anyway!
For all those how are used to play M.U.L.E. on a NTSC computer, there is the theme song that match our speedier 60Hz computer.
mule_theme_NTSC.ogg
Let me know if you like (or are you all PAL folks here?)

Oh, Thanks for this version of the theme!