I usually start by using FindDevice from the IDEfix97 package available from Aminet. As you can see the IDE Iomega Zip 100 in this A4000 is found as a scsi.device at unit 3.
Next it's just a case of putting the file fat95 into the L drawer of Workbench and setting a suitable driver to the corresponding Device and Unit number. I use PZ1C in Workbench:Devs/DOSDrivers and edit it according to whether the Zip is on an Oktagon card or something else. Giggledisk from Aminet can also create a driver for you :-)
I leave all my Zip or Jaz disks PC formatted and don't go near them with HDToolBox myself. Using fat95 the Amiga can read/write to them just as if they were Amiga formatted. Also great for file transfer between Amiga and PC. Heck, I'm doing it right now to get that screengrab here :-D
