View the source of this page (and it's javascript) to learn how it works, and how to manipulate the player. Also check out guide.txt
Set the default volume by appending "&flashvars=volume%3D100", replacing "100" with a any number, 0-100.
Be sure to offer the user a way to stop the music if you hide the player. You can do this with the togglePlayback() function.
Muting the volume (setting it to 0) still runs the decoder in the background, thus consuming the user's resources. It is best to toggle the player using togglePlayer() rather than setVolume(0).