|Unfortunately, potato boot disks do not work with ATA100. There are special boot disks for ATA66, but they don’t help. I speak from experience here.
What I ended up doing was building a custom kernel with ATA100 support, and replacing the kernel on the potato rescue disk with that. Unfortunately, I mentioned the fact in public, but I forgot to document the procedure, so when requests started coming in for help, I wasn’t much help.
However, by using this approach, I was able to install potato, and then upgrade immediately to sid. So, if you’re ambitious and reasonably skilled, you could try to copy my approach. I can verify that it works, even if I can’t remember how any more.