From the FAQ at:
C
Program Files\IOMEGA\Common\Help\howdoi.html
How Do I Change the Iomega drive letter?
Windows® 95/98/Me Users
To change the drive letter for a removable drive:
Right click the Iomega drive icon in My Computer or Windows Explorer.
Click Properties.
Click the Drive Letter Manager tab.
A list of available drive letters displays (including network drives). Select the drive letter you want to assign to each removable device attached to your system by selecting a new drive letter in the pull-down menu box below the drive icon.
Click OK.
Restart your system for the changes to take effect.
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In my experience it takes a lot of fooling around and reboots and rarely works.