The psion cable..
The next day (yes, quite amazingly I could wait!) I connected the cable to my PC and plugged it into my 3MX. Nothing happened, except for a message in a window that asked me to install the driver. No problem, the package included a small CD with plenty of drivers on it. And no manual. I tried all drivers and nothing worked. I finally found a solution and put up a separate page with the driver that worked for me as a service to fellow Psion users. Let me come right away to the end conclusion: this is a great invention! Now I can connect both my Psion MX machines to any PC with a USB port. That is my two desktop PC's and my two notebooks. Great! (scroll down this page for the driver).