How can I play a single sound file across several slides?
For PowerPoint 207
In order to make the music play run through the slides, you should
follow the hereinafter steps:
1. Click insert -> sound -> sound from file. Select the music you want
to insert;
2. In the succeeding dialog box which say “How do you want the sound
to start in the slide show? ”, please select “ Automatically”.
3. Select "Loop Until Stopped” at the "Sound Option" above the slide,
at the same time, in the “Play Sound” item, select “play across
slide”.
After you have done the three steps above, the music you desired can
be played all over the slides.
There is an article about playing audio through a PowerPoint
presentation.
http://www.ppt-to-dvd.com/forum/viewtopic.php?p=3014#3014