I recently needed to assign a shortcut key for a macro in Powerpoint. As it does not have this capability, I searched the web and came across this page by OfficeOne, which provides an Addin for creating keyboard shortcut for Powerpoint operations and its macros.

OfficeOne Shortcut Manager 3.1 for PowerPoint

The page also provides some other Addins and Tips including more animation effects, individual slide volume control and others...
See here for the Index List!