I'm assuming that you mean HP 82350. The answer is you can't. It's sort of like asking why the Nvidia DLL doesn't work with a Matrox video card. Two completely pieces of hardware will have two completely different low level drivers. NI's GPIB-32.dll is only for NI boards and the HP driver is only for their board. You have to install the driver you got from HP (actually Agilent now) in order for the board to work. If you want your program to work with either NI or Agilent boards, you should be using VISA.