If you had mentioned the make and model number of your scope, I could have given you a definite answer, but since you didn't you're going to have to do a little searching yourself. First go to the
Instrument Driver Network. There you will find several links. You should probably browse the ones under the Learn topic first to get an idea of what an instrument driver is. Then you can go to the Search link and try and find a driver for your particular scope. If you find one and assuming that your NI GPIB card is configured, you should be all set. If there is no driver, you'll have to do some programming yourself. You can use the Instrument I/O Assistant on the Instrument I/O palette (LV 7 or higher)
or follow the links under Develop on the IDN page.