You can format, read and write to zip from the OS with newer versions of MacOS. Just format it like any floppy/hard drive with the usual Mac utilities.
Iomega tools came with certain versions of Mac OS on the Install CD. If you have a CD for System7.5/8x look for it on there and on Boxed versions of MacOS.
If you are using System7.1 you can upgrade to 7.5 or better, or download Iomega Zip Tools version 5.0.3
(or whatever Iomega recommends now). This is from MIT's Mac application super-archive, and if you're working with older Macs you probably need to know about it; it's the first place to look for older Mac Software that may be pulled from sites by now. The root archive is here.
The Guest program used to be on all pre-formatted zip disks, and the first zip disks came with a floppy for basic installation of the tools, with the remainder on the zip disk itself.
To manage problems with Iomega software, check out the extension conflict guide and workarounds here.
[ November 22, 2004, 10:19 AM: Message edited by: gordguide ]