I think this works with all Motorola SM56 modems. I used it with the Motorola MOT PCI 3 chip. The other drivers I tried for the MOT PCI 3 chip where hard to install and kept asking me to change the country setting to the UK, which I found was typical of the older versions.
Got it from the TP-LINK site for their TM-IP5600 modem. It works for 98 through Vista. The download extracts to a 'MOTOROLA' FOLDER. Then run SSETUP.EXE within that folder to install the driver files--don't go through 'reinstall driver', 'add new hardware' or 'new hardware found' to do the install. If you have other drivers already installed for it you should probably uninstall them before installing these.