I just finished wrestling with a similar problem on a Win98 machine. When I ran the 'VISA Interactive Control' in the National Instruments>>VISA folder I got an 'Unknown Device' which was the serial port I was trying to communicate with. When I closed the 'VISA Interactive Control' application and ran NI MAX v2.03 etc I could browse the Devices and Interfaces>>Ports and see COM1. At first I couldn't use it (various errors when I right click and then Open Session), but after I looked at the properties (right click and then Properties) then I could open a test session, and after that everything seemed to be ok. Maybe there is something behind the scenes that writes an entry into the System Registry, but I didn't explore it further since everything is working now!