How Well Does The Powerlite S6 Projector Work Why Does My Notebook's Screen Change Resolutions Whenever I Connect My Video Beam/projector To It?

Why does my notebook's screen change resolutions whenever i connect my video beam/projector to it? - how well does the powerlite s6 projector work

I have an HP laptop, Intel Centrino Duo, Windows Vista, 4GB of RAM, and put my Epson EMP 765c Width / video projector to the screen resolution changes to lowest setting, and when I drag GUN returns Projector normal, why that's what happened, you can help me, friends?