Is it a canon problem? I found that my avi's could only be read with the software that comes with the camera, that then can export to something that is readable by all.
But this worked for me but might not for you.
Change the .avi to a .mpg extention. Its baffeled me how it works, the contents is still exactly the same way but the aproach to reading it must chage.
However i could view them in Media player + Quicktime, it was Abd Prem that was causing the problem, and thats how i solved it.
Winamp play vids?