Hi Matt, I have just bought a powerbook and am seeing the same errors that you saw. ie. "hda: lost interrupt". This must be a kernel issue as I am using yaboot to boot the linuxppc cd. I have successfully installed debian on a G4. I did this by putting appropriate kernels and ramdisk images onto a zip disk and booting from it. I'm not sure if I can do something similar with the powerbook. It doesn't have a zip disk or a floppy drive, though I do have access to a usb floppy drive at work.
Did you boot from floppy boot disks to install debian on your powerbook (firewire). Thanks, Brendan Simon.