That must be a fairly interesting avi file if movie maker can not open it. Is there a chance you could get another avi file that movie maker would be happier with? Other then that you could reencode the avi file so Windows Movie Maker is happier with it.
VirtualDub is a good one I like that should be able to get the job done.
I am not to experienced with Movie maker or how it works in releation to using codecs. I am more of a video encoder then an editor. When I get home I might try to google your problem more, but hopefully someone else might beable to help.
P,S. Lucky you dont live in Australia. Because it is 1:15pm Thursday ATM