FYI: The latest Quicktime Player has the ability to play those old AVI clips... I just tried it myself.
My suggestion: Download and install the latest Quicktime Player (www.apple.com/quicktime). Then go into the preferences and set it to be the default player for AVI files. Next time you click on an AVI file, it will be opened by the Quicktime Player instead of Windows Media Player.
Good luck!
Sincerely,
Jonathan Atkinson