I use two Beige G3 machines (now upgraded to G4's) and both have had the problem that when I use Startup Disk on System Preferences to go back to OS9, I can't get back to OS X. It appears that the Startup Disk control panel in OS9 never actually writes the correct Open Firmware values to the nvram. Several times I got back to normal by doing a OSX reinstall -- suffering the whole process just to get the nvram fixed.
Today, I found the painfully simple answer -- download System Disk 2.6.2 from Apple's download site and use it instead of the Startup Disk control panel. This worked perfectly...

