Ok, so I've cleared up a bit of the mystery.

My particular interest was getting tapes to boot so that was where I 
concentrated my investigation.

The directory src/distrib/vax/inst is where the file 
'bootroot-${release).fs' is supposed to be built.

The way it used to be built (in 1.4) was to take four files:
	edlabel (built in ./src/sys/arch/vax/boot)
	copy	(built in ./src/sys/arch/vax/boot)
	boot	(built in ./src/sys/arch/vax/boot/boot)
	xxboot	(built in ./src/sys/arch/vax/xxboot)

Create a virtual disk image using the vn driver (see vnconfig(8)) and 
install on it 'xxboot' (this writes the boot block), boot (this is the 
second stage booter), edlabel (used to be used to label disks), and copy 
(which would copy the miniroot.fs on to a disk).

This has all gone away, and it would seem that no one has had the time to 
replace it. Why did it go away?

It seems that the new booter now talks to the VAX boot device routines in 
the monitor firmware. This is a good thing since that means anything your 
VAX can boot can be used to get the NetBSD kernel into memory. However, no 
one seems to have written a program that can get the miniroot into memory 
using the new booter.

It appears that what is needed is a standalone program that once loaded, 
knows about VAXen enough to get the install kernel loaded, and once that is 
loaded the install kernel needs to know how to get the release off of the 
various forms of media.

I have no idea how you would go about doing this.

--Chuck