The double-Help menu is not a QuickTime bug, it is a DivX codec bug. This bug is fixed in the new DivX Fusion codec which is currently in beta. It is available for download and works well.
That's the link for 5.2.1 The Divx 6 beta is available at http://labs.divx.com. Divx 5 is not compatible with QuickTime 7.0.2, and the Divx 6 beta is significantly slower (which is to be expected from a beta). So you might want to stick with 7.0.1 for now. Just so you know.
Using DivX 5.2.1 does not make your Mac go up in smoke. It displays double Help menus. Some find it annoying, but I don't mind. With the DivX Fusion codec, the double Help menus are gone.