You should find good advice here:
http://www.awesomebackgrounds.com/powerpointlooping.htm
It is written for Windows, but it should work just as well on the Mac.
--David

Signature
David M. Marcovitz
Microsoft PowerPoint MVP
Director of Graduate Programs in Educational Technology
Loyola College in Maryland
Author of _Powerful PowerPoint for Educators_
http://www.PowerfulPowerPoint.com/
> Is there a way to loop one slide automatically but then be able to mouse
> click to the next slide when you need to?