Let's say you want to dual boot Linux and Mac OS 9 on that relative's shiny old iBook that's been sitting around gathering dust to show her that, no, the technology doesn't control you, you control the technology. Let's also say that Debian's developers don't tell you that installing Debian on a machine with another partition already housing Mac OS 9 will cause said partition to disappear. What happens? Chaos! Mass hysteria! People at each other's throats, civililation as we know it collapsing before our eyes...
Okay, maybe Debian PPC doesn't have enough users for that to happen, but it would've been nice to know that installing Debian on a two partition, dual boot drive would have the above effect ahead of time. It would have saved me a lot of panic and subsequent googling of phrases like "Debian Mac OS nuked" and "Debian ate my Mac OS." I would have also presumably known that the solution is incredibly simple assuming you have your original Mac OS install disks.
The partition doesn't actually disappear, mind you. You can still "see" it when booted into Debian by mounting the partition. But it no longer functions as a boot volume. Not in yaboot. Not even in Open Firmware will it recognize it as a boot volume.
So here's how you fix it. Start up with the Mac OS install disk and, from Drive Setup, update drivers. That's it. Done. I guess the partition program in the Debian installer somehow flutzes up the driver partitions, but updating the drivers solves it. I hope I saved someone out there some time.