You need to boot by doing this:

Go into open firmware (hold down command-option-O-F).

Type 'boot fd:0' at the prompt.

Just popping the disk in the drive and switch the computer on doesn't
cut it, as that loads the mac ROMs before it starts looking at
devices (and the mac ROMs have no clue what to make of kernfs, so they
just eject the disk).

       ~ g r @ eclipsed.net