Hi Davide
Have you tried running MAX (Measurement and Automation Explorer)? From here you should be able to see the various interface that you have on your system, and with the GPIB, if you have instruments connected, you should be able to scan the bus to see what is available. Also, silly question perhaps, but have you run the GPIB setup to tell the system the type of GPIB card that is connected??
Cheers
JB