Ok, trying to boot from my TK70. The problem was the block size, I set it 
to 512 like so:
	dd if=miniroot.fs of=/dev/rmt8 bs=512
and wrote the miniroot filesystem out to tape. That works fine, then I boot 
it and after much grinding it gets to the booter and trys to boot, however 
it trys netbsd first. That fails (the file is netbsd.gz) and then it trys 
netbsd.gz. Now the interesting bit is that when it trys to boot the error 
it prints is:
	nfs_open: Must mount first
That is a really weird message. It seems like the booter isn't telling 
somebody that the boot device was MUA0. Can someone point in a likely 
direction?

When it finally gives up and gives me the > prompt I try
	boot mt()netbsd.gz
and that fails with the same message "nfs_open: blah blah"

--Chuck