Hi Adrian,
You should try to install one of the Yaboot images to make sure there is no problem with your machine.That could be a check to perform... where is the last working yaboot image to be found?See: https://cdimage.debian.org/cdimage/ports/10.0/
I tried once again and edited partition manually: I created a separate /boot partition formatted ext3. The system installed and yaboot works just fine.
I am upgrading it to unstable as I type. The first upgrade had a hiccup dropping me to emergency mode, but inside there I was able to do a dist-upgrade of the base system and the system resurrected.
I have a very base system, but it boots fine - I'd say no strange
problems with this machine. I'll try installing some stuff,
including X11, sshd server, compilers, etc.
Riccardo