SteveH,
I'm sorry to hear how much trouble you had trying to install Linux on your Titanium PowerBook. I just bought a Titanium PowerBook on eBay this week, and I also encountered the problem of not being able to boot from Linux optical discs - even though the PowerBook boots from a Mac OS DVD, when I press "c" or "alt" during start-up.
But I found a solution! This involved using my iMac (which can boot Debian CDs) to install a PPC Linux system on an external FireWire hard drive. I had done that before, just to not use the loud internal hard drive. Again, I mainly followed this tutorial:
http://www.howtoforge.com/boot_debian_f ... l_firewireThis time I had to manually mount /target (and/target/dev, and /target/proc) before the chroot, though.
Then, using this system on the firewire hard drive on the PowerBook (and the chroot tricks again), I installed yaboot on the PowerBook's internal hard drive (which, in my case, had a Ubuntu 9.04 on it anyway - but I could have copied it from the firewire drive or some other media just as well).
I prefer Ubuntu and Debian over YellowDog (which I also tried because it includes libfreevec) for a number of reasons: more packages, less outdated packages, faster and more flexible (IMHO) package manager, working "fdisk -l" with Apple partitions, better yaboot configuration (taking into account existing Linux systems), ...
It might be possible to achieve similar results using the FireWire target mode, as you suggested, but I'm not sure about that, since the target /dev/sda would later become /dev/hda, when booting the PowerBook.
Another option might be the bootloader grub2, which should be a lot more flexible than yaboot.
Send me a message, if you'd like to see my kernel config and/or yaboot.conf!
If you don't have a second PPC system, a virtual system like qemu might also do the job. That would be more work again, of course...
Good luck!