I'm not sure that this will work with text or other objects on the slide, but
John Langhans of Microsoft recently posted this:
If you are using PowerPoint 2003, you can get Windows Media Player
visualizations to accompany your audio in PowerPoint by doing the following:
In Windows Media Player:
1) Create and save a playlist which contains the audio file(s) that you
want to play.
2) Play the playlist
3) Select the visualization you want to display while it's playing.
4) Close Windows Media Player
In PowerPoint:
5) Insert -> Movies and Sounds -> Sound from file... to insert the playlist
into current slide (may have to choose to view "All files (*.*)")
6) Resize/Position the resulting 3:4 (aspect ratio) visualization frame
where you want it to appear during slide show
7) Verify and/or change any of its animation or media settings using the
Custom Animation taskpane or the Edit Movie command (PowerPoint treats
inserted playlists as inserted movies).
8) Play the slide show.
NOTE: The visualization used will depend on the system you are on when
displaying the show since it comes from system (Windows Media Player)
settings on the system and is not stored in the presentation in any way.