Just in case its any help to others, I have got the found the MX-850 will communicate from a Windows 7 pc using the Belkin F5U103 Serial to USB adaptor, but you need to install a seperate driver not the one on the Belkin CD.
The driver is
[Link: techspotting.org]PL2303_Prolific_DriverInstaller_v1417.exe
Keith