I couldn't find an instrument driver for the E4402B on NI's website, so I would first suggest contacting the vendor. If you get an instrument driver, it will be much easier to program. If they do not have one, you will need to make bus calls. For instance, if it's GPIB, you will need to know that commands which the device accepts and then make 488.2 or VISA calls to the instrument.
J.R. Allen