WMP does not support AVI. You'll need another player such as Pocket MVP. You'll also need to make sure that you didn't use a codec that is not supported by a PPC player. My digital camera makes avi's using the MJPEG codec which cannot be played on any Pocket PC. What I would do is follow this thread for a better solution.
http://www.aximsite.com/boards/showt...&threadid=3692