Sorry for the repost, but I got a little more information just now.  I 
booted using the 1.6.1 installer CD, and used disklabel to get these 
values for sd0:

bytes/sector: 512
sectors/track: 63
track/cylinder: 255
sectors/cylinder: 16065 (1)
total cylinders: 521
total sectors: 8380080 (2)

(1) is indeed the product of the previous two numbers, but (1) * total 
cylinders gives 8369865, not (2).  What is going on?  Can I just set 
all these values arbitrarily?  Is there a recommended (or automatic) way 
to find the optimum setting?

When I try to do the newfs step in the NetBSD installation program, it 
gives the (paraphrased) error "With 16065 sectors/cylinder, the minimum 
cylinders/group is 64.  This requires the block size to change from 8K to 
32K, and the fragment size to change from 1K to 4K."

Thanks very much for any answers or pointers to documentation.

Arlie Capps