i haven't looked at the command set for the 8903 in a while, but with the sparkfun GPIB to USB dongle if you get a terminal program you can build scripts to send the commands to the 8903 to do a series of measurements and just capture the data as text on the terminal. feed that data into excel and you have graphs.
if you are comfortable accessing the serial port you can use any general purpose programming language to send the commands and receive the data, then process it into graphs. most of the work comes in figuring out the commands and timing, and then what to do with the data.
some of that work is done for you in environments like labview or vee that have profiles for the instruments built in and graphing functions. but as stated in the sparkfun faq, pmillet's program (and most others you'll find) were written for the national instruments GPIB controller and won't work on the sparkfun one without some modification.
ed