Doc Searls links to a piece by Derek Miller who questions the need to use presentation software like Powerpoint or Keynote at all, just use HTML pages, its the message that matters.
Here is a tip if you want to do this with Internet Eplorer on Windows. Locate the executable file for Explorer (IEXPLORE.EXE not a desktop shortcut), create a shortcut and add a -k flag to the target properties (e.g. “C:\Program Files\Internet Explorer\IEXPLORE.EXE” -k). This will run your browser full screen without chrome, as designed for use in kiosks, ideal for presentations. Ctrl W to shut it down.