Possible solution:
You must install the firmware update before installing Mac OS 9.
1. Start up the computer from its hard disk (not from the Mac OS 9 Install CD).
2. Follow the instructions for updating your firmware in the CD Extras folder on your Mac OS CD.
3. After the computer's firmware has been updated, start up the computer from the Mac OS 9 Install CD and proceed with the installation.
When you update the firmware, certain modifications are made to the System Folder. When your computer is started up from the Mac OS 9 install disc, the firmware program is unable to make those modifications because the disc is locked.