If you're having issues with hardlocking before the end, you need to delete the /System Folder/Extensions/Multiprocessing folder.
Here's my personal most painless method of installing OS 9 on this machine; no Open Firmware fiddling required. (unless my guide doesn't work)
Please tell me if this doesn't work for you, and how, so I can update this post. (for context this was done for a X 10.3 and OS 9 dual boot setup.)
0. Have an extra partition on your drive for 9.
1. Burn the
Unsupported G4s CD.
2. Boot up X and download the two links at the top of the first post in this thread. (
tbxi-enabler and
ATI,Merlin)
3. Restore the .img file from the Unsupported G4s CD to your partition with Disk Utility.
4. Delete /System Folder/Mac OS ROM.
5. Copy tbxi-enabler into /System Folder.
6. Copy the contents of ATI,Merlin into /System Folder/Extensions, overwriting the existing files. (that's the point)
Mac OS 9 will
not boot yet. Open Firmware will be able to boot to the new Mac OS ROM, but will not detect your hard drive, just showing a blinking ? floppy.
7. Make sure the Unsupported G4s CD is still inserted. Reboot and hold Option to go into the boot menu, and boot to the (probably unlabelled) hard drive w/ Finder icon. (Your OS 9 partition.)
After about 1 or 2 minutes, Mac OS ROM will give up on booting to your drive and boot to the Unsupported G4s disc. (this saves a step in Open Firmware, and if you type at my slightly above average speed that's still faster.)
8. Close the Read Me and select your main drive (should be ATA, not ATAPI... probably the second one in the list), do NOT Initialize it.
9. Click the "Functions" drop down menu on the menu bar and click "Update Drivers".
10. Allow your machine to boot into X as normal.
11. Go to the Startup Disk settings under System Preferences, select "Mac OS 9.2.2 on (your OS 9 partition)", and restart. Your machine should now directly boot into OS 9.