Seeing as this old thread has already been bumped, I should add that the SimpleViewer skin now supports background music in the form of a MP3 track played using Dewplayer v1.9 from
http://www.alsacreations.fr/dewplayer
The user has the option via the skin's 'Dewplayer' tab to choose a path to an MP3 track or to pick a track from a local drive that will then be automatically copied across into the generated album. The player itself can be positioned anywhere on the page.
No tweaking of code is required after the album is generated.