Adnan,
National Instruments provides a straightfoward installation procedure for most of our GPIB boards in the more popular OS's. I would suggest going to:
http://www.ni.com/support/gpib/
From this link, you will select your board (AT-GPIB/TNT) and your OS. Follow each instruction exactly in order to minimize your chance of failure.
Ryan Mosley
National Instruments, Applications Engineer
http://www.ni.com/exchange