Seeing that you're not getting many replies, I jump in, but beware: I'm no expert. My thoughts: as long as you're booted into Mac # 1 and try to install a bootloader to Mac # 2 mounted as Target Disk, this will fail because yaboot either can't figure out the open firmware (of for short) path to the hard disk of # 2 or will give an incorrect path. What you could try:
1. boot off of CD with your iBook in target disk mode.
2. chroot into the target disk:
find out what /dev nodes point to the target disk. Let's say this is /dev/sda. then do:
sudo mkdir /mnt/ubuntu
sudo mount /dev/sda3 /mnt/ubuntu
sudo mount -t proc none /mnt/ubuntu/proc
sudo mount -o bind /dev /mnt/ubuntu/dev
sudo chroot /mnt/ubuntu /bin/bash
3. Now head into /etc, write a yaboot.config:
Code:
boot=/dev/hda2
device=hd:
partition=3
ofboot=hd:2
root=/dev/hda3
timeout=100
install=/usr/lib/yaboot/yaboot
magicboot=/usr/lib/yaboot/ofboot
enablecdboot
enableofboot
image=/boot/vmlinux
label=Linux
root=/dev/hda3
initrd=/boot/initrd.img
partition=3
read-only
After writing this file to /etc, run
mkofboot -v
Alternatively, you could also try lilo, which I find a bit easier to use, though you'd need to install it first (in your chrooted environment, of course), it's not part of the livecd, AFAIK.
4. When you've run mkofboot successfully, exit chroot, unmount all the mounted partitions etc. and try to restart your iBook.
Good luck!