CodecViewer is a little tool, which tells you which audio and video codecs you need for an avi file.
Then I had to try every codec I can find... now I know which one I need :) ( you can also pass the name of the file as a command line option )
Program says "Unknown" codec ?
Seems as if you are using a codec, which is not supported by M$, and I don't know...
I got very often the problem, that a movie i downloaded did not work correctly, because I didn't have the matching codec installed.