In my experience, when using an internal ide ZIP drive you had to set it up using Hdtoolbox, even if it was later to be removed and another drive inserted, all you needed to do was 'mount' the new drive into the system (make sure all your ZIP disks have been pre-preped using Hdtoolbox)
I used the IDEFix97 software tho, which allowed for the ZIP drive to be swapped with little problems regarding AmigaOS getting confused.
Az
