I've never really tried this before, but it appears as though the
screensaver feature is disabled while in Slide Show Mode. Why would you
want the screen saver to appear while you are showing your presentation? If
all you want to do is to save your screen on long breaks, you can press "b"
to black out your screen while on a break, then press "b" when you come
back. "w" also works to white out your screen.
See
Ading Display Saver - This nifty utitily allows your normal screen saver to work during Power Point screen shows.
Something that is not normally possible
