Not to bother.
OK - you've maybe guessed this is a pet hate of mine. But think for a minute. Suppose somebody visits your site from a library, or an open plan office, and suddenly they find music blaring out, disturbing not only them but everyone around them, how do you think they'll respond? Stay and enjoy the music or leave your site immediately, probably never to return? This article gives a good explanation of other reasons not to use this approach.
A much better idea is to give your visitors the option to turn the music on, if they so wish, rather than to auto-play and leave people struggling for a way to turn it off. I've never used it, but something like jplayer might be the way to go.