Use DD in Linux or Windows to make dumps of the disks and then start working from those. Check out what is in the beginning with a hex editor.. If the filesystem starts right away, you can try adding the images as a normal hdf.
http://www.chrysocome.net/dd
Edit: bad advice below, I mistakenly remebered they had a physical write protect tab when I wrote this.
Write protect your zip disks before doing anything to them if you haven't done this several times before (and it doesn't hurt even then).