I discovered this morning a handy tool if you are having problems with avi files, as to which codec it uses. Here is a free download nifty tool that you can use to determine which codec it uses, and better yet if you do not have that codec, this program will direct you to the site to download it.

http://www.techtv.com/callforhelp/freefile/story/0,24330,3590754,00.html