The first step would be to figure out how to do the testing manually using the Keithley instrument. Next, look in the manual for the GPIB commands that would make the instrument do the same thing under computer control. Finally, write a program in LV that sends those commands to the instrument one at a time.
This should get you something that at least does a basic test. Add a bit of code to save the results to a file or plot them out and you should just about be done.
I know this is rather general advice but if you could provide a few more details we could give more specific answers.
Mike...
