Go to VersionTracker.com, and download Video LAN Client. This should open up almost all avi files.
If it still doesn't work, download MPlayer. This works through the Terminal, so it most definetely will play all uncorrupted avi files. The bad thing about this is that it only plays at fullscreen, and you can't forward or rewind.
for a while, if you had the right combination of components (i think it was qt5 and divx.com or jamby codec) you could change the file type of the avi movies from VfW to DIVX and quicktime would play them perfectly, no artifacts, sound bugs, or anything. i think after qt6 came out, this trick no longer worked, so vlc is the only way to play divx files without modification.