OK, I know I had mentioned this in the links I sent you. Once the installation is done, DON'T REBOOT. You need to mount the Macintosh partition in order to copy the kernel and initrd image that was installed in /boot by Ubuntu. This is probably why you've ben having problems with all of the Linux distros on this Mac. It drove me nuts for weeks trying to figure this out on my own.
In detail: When the installer tells you to reboot, DON'T. Alt-F2 will give you a command shell where you will do your damage-uh, I mean, dirty work.
Once at the command prompt, you are going to have to load the HFS (or HFS+ if your Mac partition is formatted that way) kernel module that was just installed. However, you are going to have to COPY the kernel module from the location in the /target directory (this is what will eventually be your / directory once the system boots on its own) to the exact location where the kernel module would reside in the installer's / directory.
cp -v /target/lib/modules/<kernel-version>/kernel/fs/hfs/hfs.ko /lib/modules/<kernel-version>/kernel/fs/hfs
(You might have to create the hfs directory on the latter location if it's not there. If you used HFS+, then replace "hfs" with "hfsplus" when making the command.)
Once you've done this successfully, do a "depmod -a" to make those modules available to the installer's loaded kernel. After that, do a "modprobe hfs" (or "modprobe hfsplus" if using HFS+) to load the module you just copied over.
Now you'll mount the Mac partition. Create a directory in / and call it whatever you want (I'll use "macpart" as an example). You'll then mount the Mac partition in this format:
mount -t hfs <hfs-partition-name> /macpart
(or mount -t hfsplus <hfsplus-partition-name> /macpart if using HFS+)
Make sure you know what your actual Mac OS partition is. I'm sure you saw many partitions during the disk partitioning phase of the installation. The one to point to is usually the last one, but make sure. My StarMax, for example, has two Mac OS partitions so I can choose to use /dev/hda6 which is the main Mac OS system partition in HFS+ and /dev/hda7 which is a non-system Mac OS partition in regular HFS. I did this personally as a backup measure in case HFS+ wasn't supported properly. But it should be now.
Once the Mac OS partition is mounted, begin to copy the kernel and initrd image in
/target/boot over to the mounted partition (in this case "/macpart"):
cp -v /target/boot/<kernel-image> /macpart
cp -v /target/boot/<initrd-image> /macpart
Be sure you don't copy the syslink instead of the actual kernel and initrd image. To be sure of which files to copy, "cd" into /target/boot and do an "ls -l" before copying over. This will show you which is a syslink and what actual file it is pointing to.
DO a "cd" into your mounted partition directory (in this case, "/macpart") and verify that the files are in there. If they are, "cd" back to / and unmount the Mac OS partition (umount /macpart). Hit Alt-F1 and you'll be back at the screen of the installer. Allow the installer to reboot and allow the PowerBook to boot into the Mac OS desktop.
Once there, you should see the files in the Macintosh HD. Move the kernel image over to System Folder-->Linux Kernels. The initrd image can be wherever you want it (I usually put it in the same place as the kernel). Delete the kernel you used for the installation or rename it so as not to be confused. Launch BootX and select the kernel you just copied over from the Linux partition. Also make sure you select the initrd image you also copied from that Linux partition from within "Options" in BootX. Once these are set, save the preferences and boot into Linux. Hopefully you'll see the desktop.
If all you get is a blank screen or a screen with some weird characters, then it's posssible that you need to pass a kernel argument from within bootx to allow you to view the console text on boot. In the "More kernel arguments:" section, type the following:
That should give you output of the bootup into Linux. If not, then you might need to add some resolution options manually. Here's the link to the Linux PowerPC FAQ-o-matic with all the information you need to pass resolution and color depth information in the kernel arguments section:
http://www.jonh.net/lppcfom-serve/cache/1043.html
I think this will cover everything you need to get it going. Once you're used to the process, it's a piece of cake. Incidentally, I've taken on the task of learning FreeBSD on an x86 machine I have. Talk about feeling like a n00b! If you have any experience on that, I'd be happy to pick your brain.