Saw this old thread today and it brought back an old trouble shooting memory.
I think what I mention below might explain some of the problems that folks in this thread reported.
This was my experience on an MDD.
With the ATI drivers which are installed with the OS 9.2.2 update, QuickTime 6.0.3 will lock up the machine during extension loading. The mouse will move but clicking the mouse and typing on the keyboard will have no effect.
The culprit is ATI Video Accelerator 4.8.5. Update to 4.8.7 by installing the January 2005 ATI OS 9 Mac Software Update. If you have an nVidia card, this probably isn't a problem. This experience occurred with a Radeon 9000.