Here you go:
iMovie only reads AVI that both the audio and the video were compressed by using a codec that iMovie can recognize. If your AVI video files are not imported, it's because of the codec used to create the AVI file is not supported by iMovie, even if you have Perian installed, which only allows you to play AVI in QuickTime. If you want to edit AVI in iMovie, the easy option would be converting the AVI files to an iMovie compatible format, like MOV, MP4, or M4V.
To achieve this try using "Any Video Converter" available from the App Store for free then import into iVideo.
Cheers