boot problem

I just got myself stuck as I had a working aout kernel+userland, but just
changed the kernel to elf, and now libs aren't happy, so solution: try to
boot an install kernel. (Note in passing: for some reason my SparkPlug was
happy to untar, but not uncompress the BtNetBSD.tar.Z file)

I get the count down, then start! Then nothing, all freezes, blue button
time. 4.1 of prep.RISCOS just says "edit the `fastboot' file". Was it
sufficient therefore just to

Set NetBSD$Kernel :5.$.new.netbsd.INSTALL

?

Where is NetBSD$Root used? (Can't find it referenced - should it be
/dev/md0a for an INSTALL)
What is installation/misc/ramdisk.fs.gz for?
What NetBSD$BootOptions exist? (I find symtab and oldkernel referenced in
BtNetBSD, but not maxproc nor noftp)
Is there a way of saying "single user mode please?"?

Anyway, I then tried varying wimpslots up to 20000k, but still nothing, just
the Start!

Any clues?

Cheers,

Patrick
(Tried subscribing yet again...)