Which Video Codec?

Hello,
I downloaded an episode of a TV show in AVI format, but it doesn't run (no audio or video). I assume that I don't have the right codec, but I don't know which codec to install. Is there some kind of program that will read the header info in an AVI (is there header info?) and tell me what codec is needed?

Thanks
-George

Try installing DivX or XviD. They are the big ones.

Also, get the kazaa codec pack and search for a program called gspot (also from kazaa), gspot tells you which codec(s) a movie file uses.