Many drivers can be found on NI's Instrument Driver network located at: http://www.ni.com/devzone/idnet/default.htm. Unfortunately, there is not one for the LeCroy LC684DXL. You may submit a request for this driver. This is one of the options provided on the webpage listed above.
Since the driver is not currently available, you will need to write the commands GPIB commands to control the LeCroy LC684DXL. This can be done by using the GPIB VIs or by using the Instrument I/O assistant. You may find the Instrument I/O assistant easier to work with because you can easily step through your program.
