HUGE THANKS goes to Scott Simmons over at the Edit Blog.

If you have trouble with ANY recent Quicktime update…specifically QT 7.4 or QT 7.3, The solution is to go back to a previous version of Quicktime. Apple still hosts them, and Scott dug them up. The name of the link has the version number is listed in the link. And if you don’t want to do an Archive and Install of the old OS, you can use Pacifist to remove QT before you install the one you want.