/*******************
  Copyright (c) 2004-2012 TinyWebGallery
  written by Michael Dempfle
  TWG version: 1.8
  Web site: http://www.tinywebgallery.com
********************/

Please read the instructions on the website how to use the mp3 background music.
You maybe have to adopt the path to the mp3 if you have your pictures directory somewhere else.
You need to change e.g. 

html/mediaplayer.swf?file=pictures/{directory_name}/background.mp3
to 
twg/html/mediaplayer.swf?file=twg/pictures/{directory_name}/background.mp3

twice in the file. The path to the player AND to the mp3 has to be changed.