Looks neat, but a couple of things...
- You only need a "global" declaration when you intend to assign to a global variable (and that variable is not mutable, like a list, dictionary, or some custom object).
- Using "urlparse" to decode the URL may be a good idea (especially for "setTrack.cmd" and __substitute).
- If you're not going to use a template language, at least use a library like lxml to generate correct, well-formed XHTML (your expression will also be much clearer using lxml's builder syntax).
You could also probably simplify it a little by using cherrypy (or similar) to handle the HTTP server, and separate your jukebox logic into another class (and get rid of all those globals in the process).
Good luck!