AVIs use many different (MPEG-4 mainly) codecs to play files;
This tool (AVICodec) will tell you exactly which codec you need to play the file. And then you can pick up the codec you want from
here (www.free-codecs.com).
Also a tool you can install on the codec site is called "FFDShow MPEG-4". That is a universal MPEG-4 decoder that can render a lot of .avi files that you may view.