I'm struggling a bit.  If I do mbrlabel, I get a disklabel
that includes the BIOS level partitions.  I can mount the
DOS partition successfully (presumably a good sign), but
then sysinst complains about it being mounted (and besides,
sysinstall seems to build its own disklabel that applies
just to the BSD partitions within the BIOS NetBSD partition*
I tried to follow the FAQ instructions in the hope of
editing sysinst's disklabel to include the FAT16 partition,
but setenv didn't work so I'm going to have to learn ed.

Any helpful advice would be most welcome right now, I'm off
to force myself to learn ed.

                           * unless wd0d is the entire disk.