Vostro 1500 (Nvidia Geforce 8600) and 2400MP projector display

Just received and connected these 2 pieces of equipment. How do I set the monitor display to activate the notebook display and  the projector display simultaneously? I toggle the settings using FN and F8 but I can only get either the projector or notebook to display independently. I wish to operate a 3D modeling program called Sketchup on the notebook monitor and the projector simultaneously. I am able to operate the program when it is displayed on the wall but would like to see the image on the notebook screen as well.