"S.J. Borrill" <sjb42@cus.cam.ac.uk>  wrote:
 > sd0 at atapibus1 drive 1: <IOMEGA  ZIP 100       ATAPI, , 23.D> type 0
 > direct removable
 > sd0(wdc1:1): illegal request
 > sd0: drive offline
 > 
 > Trying to access /dev/sd0a says 'Device not configured', though the drive 
 > is briefly accessed the first time.

strange.  I have an atapi zip drive in one of my sharks and I was able to
newfs/mount a zip-disk just fine... Mine doesn't give that error during
boot though.  

Shot in the dark: try booting the machine with a disk in it...