NI-VISA 2.5+ has added support for HP-VISA (SICL) through an abstraction layer called TULIP. Uninstall HP-VISA if it is present on your system and then install HP-SICL (but not HP-VISA). Then install NI-VISA 2.5, reboot, and go to Measurement & Automation Explorer >> Tools >> NI-VISA >> Passport Editor. You will see seven entries there. One will be "NiVisaTulip.dll", which by default will be unselected. Select it and then hit "OK". A message will come up telling you that you have changed one or more passports and that you must refresh the Measurement & Automation Explorer. After the refresh you should be able to successfully use NI-VISA, and your HPIB board without problems.