Hello,
You should be able to find the documentation for the NationalInstrument.NI4882 object embedded in the Measurement Studio help which is integrated into the Visual Studio .NET help. Inside you will find an explanation of all the different methods, etc. Also, you can find a few example programs installed on your machine at the following location.
C:\Program Files\National Instruments\MeasurementStudio70\DotNET\Examples\GPIB
Hope this helps! Good luck with your application.
Regards,
Steven B.
Applications Engineering
National Instruments