Not sure why VLC wouldn't work for you because it will play damn near any file type. However, if you're using a Mac with Quicktime or Quicktime X then you will need a plugin called Perian to play the files. You can download it here
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If that doesn't work you can try to "fix" the .avi file with VLC. You can use Google to find instructions for that. Otherwise, you may have some corrupted files.