I hope this is the right forum for this question.

I'm trying to install MorphOS on a PowerMac with a
clean install of OS X 10.4. I've partitioned as described
in the PDF guide, and installed OS X. When I boot
the MorphOS CD and get to partitioning, the partition
manager shows me two of every partition I created under
the OS X installer. There are also a bunch of little
28k and 256k partitions scattered around. None of these
partitions are usable by the installer, which pops up a
little bubble telling me the max size of the partition
is zero.

Have I done something wrong? Is there a workaround
for this? Any advice is appreciated.

> the partition manager shows me two of every partition
> I created under the OS X installer.

See this thread:
https://morph.zone/modules/newbb_plus/viewtopic.php?topic_id=7586&forum=9