Hi,
This is a very generic question, so I won't go into too much details.
First, you should look in www.ni.com/idnet and seartch for any available instrument driver for your instruments. If you find them you can program using the high level functions the driver provides.
If you can find the driver, you'll need the instrument's programming manual. This manual will tell you the commands necessary to operate the instrument.
To actually send the commands (Instrument I/O) you can use either the VISA library or the GPIB VIs. We recommend using the VISA library.
You can find example programs and information at
NI Developer Zone. Search for
visa gpibHope this helps.
DiegoF
National Instruments.