Where did it go?

When I plug in my USB Iomega Zip 100 drive into my Windows 2000 Pro I lose my secondary hard drive, (it still sees it) but wants to format it. Even if I then dis-connect the Zip drive (unplug) Win2000 still refuses to let me access the hard drive.Any ideas how I can have my cake (the zip drive) and eat it too (the hard drive)? Thanks in advance.