I have a 550mhz Powerbook G4 (gigabit ethernet, VGA) model. It has fresh installs of OS9.2.2 & 10.1.5. It locks up every time booting into 9.2.2 (quits at the same place. In 10.1.5 it locks intermittently depending on how long the machine has been on. First time of the day it will complete and work about 10 minutes, then its downhill from there.
A boot into "No Extensions" in 9.2.2 will allow the laptop to work, as a safe boot into OSZ 10.1.5 will. I turned all the extension on in 9.2.2 except the "ATI updater" and it works flawlessly. A safe boot into 10.1.5 will have it working well, but of course all the devices are not loaded.
I reset it, went into OF and reset the nvram, updated all ATI firmware with the latest versions, updated the Powerbooks firmware to the latest version with no effect on the problems.