There is two ways of background music, MIDI or Real Audio:

Lots of links to MIDI-files:

Get the new RealPlayer 4.0 beta.
Now one RealPlayer plays RealAudio and RealVideo. Get the
free RealPlayer or the full-featured RealPlayer Plus here:

Listen to a few classical
masterpieces in STEREO: (linking does not always work!)

Four Seasons

Eine Kleine Nachtmusik

Drottningholm Music

Lots of links to live Real audio/video stations: