I had the same problem as Diana with AVI files produced by the Canon PowerShot A620 camera. I had the same problem with my previous Canon. In SF the sound file is imported OK but not the video. I convert the file to WMV using Movie Maker and this works OK with little loss although the file is much smaller, AVI 43mb and the WAV 3mb. Not tried any of the codec suggestions other than removing the 3rd party option which had no effect.
My Sony Cybershot Camera produces a MPG file and this works fine.