I'm working on a iBook 466/192MB - OS X 10.0.1 and 9.1 on a single partition.
When I select OS X in the Startup Disk Control Panel (while in OS 9.1) I am warned that there is no system folder selected and that unpredictable things may happen.
If I reboot, OS X boots fine. Selecting Classic in the System Preferences provokes the notice that there is no MacOS 9.1 or later installed anywhere (I've got three now) so Classic cannot start. I've reinstalled OS X (& the update - 10.0.1), reinstalled 9.1 and rebuilt the desktop (in 9.1, not Classic). I can still select OS 9.1 as the startup disk from System Preferences.
I'm at a loss here. I need Classic to run some everyday stuff. Any ideas?

