So, I finally got my TiBook back from Apple repair, who kindly reinstalled MacOS. After re-erasing it and installing potato r3, I tried to boot my new Debian system, and I got the "image not found" message from yaboot.
At first, I thought I'd screwed up mkofboot, but I eventually traced this message back to the problem that on the new system, /vmlinux was a symlink to boot/vmlinux-2.2.19, which didn't exist! In fact, my whole /boot directory was empty. And just now, looking at the output of "dpkg -l 'kernel-image*'", I don't have any kernel images installed. Using OF, I was able to boot from the kernel from the CDROM with root=/dev/hda5, and from there finish the installation. One other thing; I noticed that the potato r3 CDROM booted on my TiBook, but there was just a white screen. I went into OF and booted using video=ofonly, which worked. Maybe video=ofonly could be made the default for installations? There's probably some reason it's not (I know next to nothing about the PPC world), but I thought I'd mention it.
