If it's a parallel port Zip 100, you will have to go to:
http://www.iomega.com/software/index.html
When the page loads, use the Download Wizard to direct you to the Windows XP
version of Iomegaware and the Parallel Port Slow Transfer Patch. Delete the
drive from Device Manager, install both of the downloads and the drive as
directed.
If it's a USB ZIP 100, delete it from the Device Manager, reboot, and let
Windows XP find it and install the native Windows XP drivers for the drive.
For any other ZIP drive: Delete it from the Device Manager, then use the
Download Wizard at the Iomega site to get the Windows XP software/drivers
and install as directed...