Just to clarify, the PB thinks the projector is a second display, just as if it were another screen off to the left or right of your built-in screen. If you move your mouse off one side, it should show up on the projected image. When you go into desktop preferences, it will display a menu on both screens. You can select the desktop image you want on the projected screen by navigating the prefs menu on that screen (not the one on your actual PB.) So you can set it to have the same or different background. If you want people watching the projection to see exactly what you see on your screen, go to display prefs and select "mirror displays."