I have made some progress, I think, since my earlier post about trying to
run disklabel on an external Mac Zip drive.  I now have the following
partition table:

7 partitions:
#        size    offset     fstype  [fsize bsize cpg/sgs]
 c:    196608         0     unused      0     0         # (Cyl.    0 - 95)
 g:    196512        96     4.2BSD      0     0     0   # (Cyl.    0*- 95)

I have used the interactive mode of disklabel to try to change the 
fstype of partition c to 4.2BSD.  It indicates that it is changed when
I print the partition table, however, if I write the table with 'W',
and then look at the table again, it has reverted to the above.

Of course, when I run newfs on the device, it says that the first
partition is unavailable.

Thanks for any help,
Barry