there's a great program called VLC, it plays just about anything. i hope i'm not breaking any rules doing this, but here's the link:
http://www.videolan.org/vlc/
i'm pretty sure it's free. i'm on a pc now, or else i'd test that theory. but i have it on my mac laptop, and it handles almost all the video problems i've had. it plays avi's and wmv's. hope that helps!