When two devices share the same data ribbon cable in a system that doesn't support "Cable Select," the device at the end connector of the ribbon cable is configured as "master," while the device connected to the middle connector is configured as "slave." Your optical drive likely has its configuration jumper installed as "master," so the Zip drive should have the small plastic jumper installed across the pins marked "slave." Do you primarily have 100 MB Zip disks or a mixture of 250 MB and 100 MB disks? The reason I'm asking is to determine if you've already acquired the Zip 250 drive or would prefer a Zip 100 drive? A Zip 250 drive can read and write both Zip 250 and Zip 100 disks, but erasing/reformatting a Zip 100 disk in a Zip 250 drive with the IomegaWare software takes a long time. Iomega had a tech support article about this some years ago. Since the IomegaWare software isn't compatible with OS 10.5.x, you wouldn't attempt to install it anyway. If you only need to access these Zip 100 or 250 disks for file retrieval, why not save yourself some trouble and use a USB bus-powered external Zip 250 drive. It connects to your computer via a USB cable for both power and data, so it doesn't need a separate power supply. They're no longer manufactured (as is the case with all Zip drives), but you could probably find one at eBay. I recently saw a new-in-box/sealed Zip 250 USB drive priced at $10 in a thrift store, but it had no takers for weeks. After CD-R/RW and DVD±RW disks replaced Zip 100, 250, and 750 drives as the preferred media for data backup, flash drives have gradually replaced CD and DVD burners.