This is rather involved but in PowerPoint on a Mac at least you can go to
the File menu and choose Make Movie. This creates a QT movie of the
presentation. Then assuming you have QT Pro you can open the movie and then
export it and deselect the video. With QT Pro you should be able to edit out
any thing that you don't want. I don't know of a way to do it just from
PowerPoint.

Good Luck,
Carol
-- 
Carol O. Smith
Keck Humanities Resource Center
Lawrence Hall
Colgate University
13 Oak Drive
Hamilton, NY 13346
315-228-7284

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