Can't boot installer disk on Powerbook Lombard

[Emil]

Hello

I'm trying to install the preview of 5.10 on a Powerbook G3 Lombard that
right now is running 10.3.9. I'm trying to make a clean install of
Ubuntu, no dual boot or anything.

Anyway. I can't boot from the CD. I've tried holding down 'c' and I
tried the option key. Nothing works. I selected burn image in Toast, and
 no other settings when I burned the
ubuntu-5.10-preview-install-powerpc.iso. But I shouldn't have to make
any settings, boot flags and such should be in the iso, right? Can I
somehow check if the CD is bootable?

I really wanna get this running and I don't know where to start with
such a problem.

Regards Emil