Questions of this nature should probably go to netbsd-help@netbsd.org,
rather than tech-install.

> After running copy_kernel--which claims that all is well and indeed
> does put a copy of 'netbsd' onto wd0a--and setting the boot
> partition to the NetBSD partition, the system reports 'Missing
> operating system' upon reboot.

This error can mean that the BIOS information (specifically, the
starting cylinder, track, and sector) for your NetBSD partition was
computed using a different geometry than the BIOS actually uses, so
the MBR boot loader can't find the NetBSD boot blocks.  This problem
is only likely to have happened if you created the partition using the
NetBSD fdisk when your disk had no other partitions on it.  (If there
were other partitions on the disk, the NetBSD 1.1 fdisk should have
been able to intuit the BIOS geometry from the existing partition
table entries.)  To recover from this problem, you can use pfdisk
under DOS to find out the BIOS's idea of your disk geometry, and then
use the NetBSD fdisk to display and (if necessary) update your disk's
partition table if there's an inconsistency.

Another possible problem is if you never installed boot blocks on the
disk during the NetBSD installation.  This seems unlikely if you
followed the installation procedure.  To recover from this problem,
you can simply run

	disklabel -B wd0

Neither of these problems seem very likely, but they're worth
checking.