Follow the steps below if you want to play and/or edit a downloaded slideshow:
Download the Powerpoint version of the slideshow.
Unzip the downloaded archive.
Open the Slideshow folder.
To simply play the slideshow, double-click on Play (XP & Vista only).
To edit the slideshow in Powerpoint, double-click the Powerpoint (.ppt) file. The filename will mirror the particular episode title, for e.g.: Health_3_Polio.ppt or Grammar_Counterfactuals.ppt.
Download the Keynote version of the slideshow.
Open the downloaded archive.
If you have Keynote, double-click the Keynote file.
If you have do not have Keynote installed, use Finder's built-in Quick Look feature to play the slideshow (OS X 10.5 & later): click once on the Keynote file and press space-bar to use Quick-look.