I installed my AT-GPIB board under Windows 95 according to the descriptions in www.ni.com/support/gpib/win98_95cr.htm and www.ni.com/support/gpib/at-gpib/install.htm.
As a result, the GPIB functions are working properly with LabVIEW 5.0.1, but using the VISA instrument functions causes an Windows error in "visa32.dll" and one has to close LabVIEW. However, the remaining commands in the running vi are executed properly.