Going back to the first disk I was trying to install 1.2.1 onto, 
I was getting esp timeout errors. I realized I was using a 1.2
kernel (since the 1.2.1 kernels weren't there when I first grabbed 
the sets), so I got the 1.2.1 GENERIC kernel and the esp driver
problem went away. However, now instead of 'bad magic' from 
dmesg, I get 'dmesg: kvm_read: kvm_read: Bad address'.

Wheee. :)

/usr/mdec/binstall works, although I still can't boot from
this disk. The PROM probe-scsi prints 'Target 1' a newline, and then
hangs... It's an IBM 94G2441 540MB drive. Could power problems
cause something like that? Any other ideas? The 200MB drive
works, but I'd like a little more space. I suppose I'll
have to try it in an external enclosure now.

...and that didn't work. Any other reasons the drive would
work fine but not be bootable?