powerpoint

Right click and choose to loop or, from the Help file under SoundTrack:
"Click the CD icon, right-click, and on the shortcut menu, click Custom Animation.

In the Custom Animation task pane, click the arrow on the selected item in the Custom Animation list, and then click Effect Options.

On the Effect tab, under Stop playing, do one of the following:

To stop the music on mouse-click of the slide, select On click (the default).

To stop the music after this slide, click After current slide.

To keep the music playing for several slides, click After, and then set the total number of slides the music should play on. "