I found this in a few different places around the 'net - hopefully it's helpful:

Remove Interference in Movie Files

If you have any AVI files that you saved in Windows 9x, they might have interference when opened in Windows XP. Fortunately, there is an easy fix to get rid of the interference:

• Open Windows Movie Maker.
• Click View and then Options.
• Uncheck Automatically create clips.
• Now, import the movie file that has interference and drag it onto the timeline.
• Then save the movie. During the re-rendering, the interference will be removed.