Well, I finally got the ZIP 100 drive and am able to read the MSDOS
filesystem I wrote there using a Macintosh (go figure).

The disklabel I used is slightly different from either of those suggested.
I tried Phil Knaack's suggestion, and it was almost right.  But I found that
to read my data I had to start the partition at offset 32 instead of 0 (and
make corresponding the reduction in size).  I wonder if this has to do with
the MSDOS partition table on the disk (I partitioned the disk and formatted
the MSDOS filesystem on a PC using Windows NT, and wrote the files on a
Macintosh with PC File Exchange).

type: SCSI
disk: zip100
label: zip100
flags:
bytes/sector: 512
sectors/track: 32
tracks/cylinder: 64
sectors/cylinder: 2048
cylinders: 96
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0           # milliseconds
track-to-track seek: 0  # milliseconds
drivedata: 0 

4 partitions:
#        size   offset    fstype   [fsize bsize   cpg]
  a:   196576       32     MSDOS                        # (Cyl.    0*- 95*)
  d:   196608        0    unused        0     0         # (Cyl.    0 - 95)