There are several examples shipped with the NI-488 driver. These can be found in the \languages directory. Also, LabWindows/CVI should have a couple examples for general GPIB communication.
I might also suggest searching the Developer Zone (http://zone.ni.com) for more examples.
Also, I might recommend searching through the instrument drivers to see if any code has been developed for your instrument already. The instrument driver network can be found at http://zone.ni.com/idnet97.nsf/browse/
Ryan Mosley
National Instrument, Applications Engineer
http://www.ni.com/exchange