Animated GIF's only work in PPT2000 and above. In PPT97, you can convert the GIF to an AVI, using Animation Shop that comes with Paint Shop Pro, or you can use the GIF Construction set available at http://www.mindworkshop.com/alchemy/gifcon.html..

If you know that you will not have to use the Viewer for this presentation, you should check out Quick Trick #2 at http://www.soniacoleman.com/Tutorials/PowerPoint/quicktricks.htm

For more detailed information about how animated GIFs are played in PowerPoint 2000-2003, see Animated GIFs Play Differently in Versions of PowerPoint