I need a tool like this from time to time, but I have never been able to get DivFix++ to do anything for me. It always complains that the file is not a valid AVI. I've tossed a few dozen AVIs at it, and it never works.
I always end up resorting to ffmpegX's "Fix" tool, which works about 50% of the time.
Sadly, VLC is often able to repair broken AVI headers, but it *will not save the repaired file*, so you have to allow it to "repair" the video every time you open it. How stupid is that.