Regarding the serial port cable for the HP50G, I got one from hpcalc.org and its working fine. It´s not just a cable but it has an Atmel microcontroller and a level conditioning IC, something like the max232, to convert the serial i/o to a true RS232 signal. As,far as I am concerned the cable is working ok. I am experiencing some data loss when I receive data but that has nothing to do with the Erich Rechlin's cable which is working fine. I previously used a homemade cable just for reception of Nmea strings from a GPS and, as I noticed that same characters where lost sometimes, I susptected something was wrong with my cable. Transmition, nonetheless seems to work flawlessly. I am still working on this "missing character" problem.
Regards
Bill