I read carefully the installation instructions for netbsd 3.1 on macppc 
and then tried to install the OS on an iMac G3 233MHz using a CD and 
issuing at the OpenFirmware 3 prompt:

> boot cd:,\ofwboot.xcf netbsd.
macppc

Openfirmware 3 wined that netbsd.macppc was not found and 
therefore made a request for the file to boot. 
Well, after painful 
hours of trial, re-reading of the instructions, etc I found that the 
right command for that iMac was:

> boot cd:,\ofwboot.xcf 
macppc\binary\kernel\netbsd-INSTALL.gz
(Attention- backward slash!!!)

Being this very basic and easy to understand for a beginner, I suggest 
to add a sentence in the instructions telling that if macppc.netbsd is 
not found and the mac asks for a file to boot one can type

directly 
macppc\binary\kernel\netbsd-INSTALL.gz directly at the boot: request OR 
from scratch

> boot cd:,\ofwboot.xcf macppc\binary\kernel\netbsd-
INSTALL.gz
(Again attention- backward slash!!!)

Ciao
Vittorio