Have you installed the drivers for the cable (from the CD that should've been included with the cable)?
If so, when you plug the cable into a USB port on your computer, Windows will assing a "COM port" to the cable. To determine the COM port assignment, you'll likely need to go into Device Manager (right-click on the My Computer icon on the desktop, select "Manage", then click on the "Device Manager" item). Look under "Ports (COM & LPT)". There should be an entry for a "USB Serial Port". The COM port number for that entry is what you need.
In Win97, if you're using that program, go to Configuration -> Serial Port. Select the COM port number determined above. Win97 will then let you download from / upload to the scanner (look at the "Scanner" menu).