I know I'm not the only one. Quicktime trashed my PB G3 when it expired yesterday. After trying to run quicktime, my computer would only boot with extensions off. Here's how I fixed it.
With Extensions off, open the entensions control panel. Select Mac OS Base or Mac OS all. This should get you running to remove quicktime and reinstall PR3 or QT 4.1.
Took me 2 hours to figure it out.
Stupid Apple!