Rather than resorting to a serial port monitor, it should be easier to find these instrument commands in a users manual. The user manual should also document other details regarding serial settings, communication protocol, and even possibly provide an example using thier commands to get the instrument to do something. For additional information, you can take a look at the instrument driver templates at:
http://www.ni.com/devzone/idnet/development.htm
Just make sure that you have your VISA serial settings configured properly. The templates should give you an idea of how to do this.