Just so you know, in the future Xvid and Divx make AVI files that are using the Mpeg4 format. AVI files are just container files... like Quicktime or Ogg.
For example Ogg is a container file for Vorbis music, and that's the most common, so people call it ogg vorbis, or just ogg, even though Ogg can contain many different formats, even video. For instance you have Oggs that encase Flac or Oggs that have Theora video format + Ogg audio format. Ogg Vorbis is nice, too, because it can handle up to 255 unique audio channels or something like that. But I digress.
DVD's, Digital Cable, Digital Satallite use Mpeg2 formats. So on and so forth. Just a FYI.