That feature is not supported by PowerPoint. Maybe in the next version
because it is asked for a lot. (Note: in case any MS attorneys are
listening and in case this is really in the next version: I have no
knowledge of what is in the next version, and I am not a beta tester, so
this is just speculation).
--David
--
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.loyola.edu/education/PowerfulPowerPoint/