Hi Shawn
I'm rather new here and to the Mac's also having just bought a MacBook Pro. Been on PC's for years and using Sony's Vegas Pro. So my knowledge of MAC is still quite a bit limited.
In answer to your question as far as I know (AFAIK) You have only a few choices. Use BootCamp and something like Vegas, or get Sorenson Squeeze which is available for the MAC Platform. Then you can probably import your QT file into Squeeze and encode to AVI.
Maybe try a Google search for QT to AVI on MAC and see what comes up. There's a lot of little seperate conversion programs.
I definately would NOT use DivX for that because the client may nothave that codec installed and wouldn't be able to play it.
ASX Media Group, Inc.
http://www.asxvideo.com