To determine wether your Zip drive is IDE or ATAPI, use regedt32 to browse to:
HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\Scsi\ScsiPort0\ScsiBus0\Target ID n\Logical Unit ID 0
Where the Target ID n is 1 or 2 for devices on a primary EIDE channel and 3 or 4 for devices on a secondary EIDE channel.
Inspect the Identifier value which contains manufacturer, model number, and firmware revision.
The firmware revision for an ATAPI drive has a trailing letter (IOMEGA ZIP 100 23.D)
while the IDE drive has a leading letter (IOMEGA ZIP 100 B.29).