Hello Anne.  I believe you've got the process mostly right.
However, I think you may have an off-by-one error in your dos (part0) label
and your NetBSD disk label.  Typically, you'd want the first sector of the
first usable partition to be 63, not 64.  I have found that BIOS's are
fairly unforgiving of this point and so 63 is what the magic number must be
for the first partition.  
	So, if you adjust your disklabel and fdisk partition tables to put sd0a  
with a starting point of sector 63, you should be in good shape.

	Oh, yes, one more thing.
Since you're using sd0 as your boot disk and since BIOS is reading it,
partition it as if the NetBSD geometry didn't exist.  That is, use only the
BIOS geometry when calculating your partition sizes, starting and end
points.  Although this means you might have to use a larger block size on
the FFS filesystems, the pain and agony of trying to get two different
geometries to line up on the same points when addressed with either
geometry, not to mention the agony of trying to calculate chs addressing on
both geometries when you calculate your partitions, can be neatly avoided.
So, construct your NetBSD disklabel such that it has 16065 sectors/cylinder
and slice your NetBSD partition appropriately for that geometry.

Good luck and hope that helps.
-Brian