>        So I computed these values in sectors and I gave the values
>        of NetBSD's partition size and its start sector's offset.
>        During the installation, the program asked me if I want to overwrite
>        the DOS partition. At this point I answered N and the installation
>        continued.

Here is the problem.  You will only get the "Overwrite the DOS partition" 
message if the offset you gave to the install program does not match up with
with the offset in the DOS partition table.

I've built a version of the inst-10 floppy with a new disklabel that (in
theory) will give some more diagnostic information when it encounters this
condition.  I'll send it out to anyone who wants it.

NOTE: This is completely UNOFFICIAL w.r.t the NetBSD distribution.  It also
hasn't been completely tested; it might hose up your disk or do other weird
things.  But I think it should work.

--Ken