As far as the messages in the mail, the problem seems to be in creating
iso image.

The command line I am using was
mkisofs -part -hfs -r -J -l -o CDimage directory

mkisofs is at /usr/pkgsrc/sysutils/cdrecord/
directory has files:
  macppc/
  netbsd.GENERIC_MD.gz
  netbsd.gz
  ofwboot.xcf

I think I have tested following machines.
G4/400 iBook/SE 366 iBook/Dual-USB(old) Ti-Book/550

The boot string is always 'boot cd:,ofwboot.xcf'.

By the way, do you have HFS/HFS+ partition now ?
If so, just put
  netbsd.GENERIC_MD.gz and ofwboot.xcf onto Macintosh HD
and
boot hd:,ofwboot.xcf   netbsd.GENERIC_MD.gz

---
(Makoto Fujiwara)
http://www.ki.nu/software/NetBSD/iBook2/