I also have been looking for such a converter, but haven't found one.
The only working solution i found was using Quicktime Pro to export as mpg.
But its Quicktime.
Another problem is that commercial Quicktime movies are mostly password protected (like the LOTR Trailer) so none of the other tools i tried
were able to convert the files.
Recently i found
http://www.eo-video.com/.
They say their player is able to convert
quicktime but i haven't tried it yet.