Ignoring the Mac partition support in NetBSD since it's not
complete...

NetBSD/macppc uses standard NetBSD disklabels, so you partition the
disk with disklabel. If you want to boot off it, you should run
installboot (exact invocation is given in the FAQ at least, and maybe
the install docs), which will create a vestigial Mac partition map as
well. (Which NetBSD won't use.)

> OF claimed that there was no bootable HFS partition (true enough - I 
> allocated all FFS+swap partitions). Arrrgh.

If you're booting off whatever:0, it shouldn't be looking for an HFS
partition. It's possible that installboot will do the wrong thing
somehow if you run it on a disk that already has a Mac partition map.
(I'm not sure.)

> Which MacOS tool to use for that?

There's no MacOS tool currently in existence that will let you set up
the disk to be NetBSD-bootable.

-- Dan