AVI is just a common use extension for videos that have the video and the audio interleaved.
The codec inside is a different issue.
Where did you get the video? From a camera? From the Internet?
If you download MediaInfo install it, and drop your video on it, then post a screen shot of the results, we might be able to offer you some advice.
Be aware that DivX is not supported.
Edit: John beat me to the punch