I'm surprised that Iomega cannot help you with their own products, however old they may be.
But perhaps the software in the site linked below may help. It seems to offer various Iomega 1-step software, and if you can remember what you used all that time ago, perhaps you can use the same again;
1] The software is not compatible with the OS you are currently using.
2] If that original Iomega software backed up these files with password control, you may struggle to get this software to work, even if you know the original passwords.
I have recently discovered some old zip discs that I created years ago of photos that I had taken and would now love to retrieve. I bought a iomega zip drive off ebay but have now discovered I am unable to open the files as they are '1-step' files. I've been in touch with iomega but they couldn't help. Can anyone suggest how I can find the software that will enable me to open my files?