First, connect your projector to one of the hdmi output of the video card. Configure Windows extend the desktop and use the projector as a secondary monitor (Control Panel\Appearance and Personalization\Display\Screen Resolution).
You can undock Sequence Preview window by click the small icon on it's top-right (looks like two squares with an arrow).
Once the window is undocked, you can move it to another monitor (the projector).
You can also double click on the Sequence Preview window which bring up the Actual Preview window which allow you to expend to full screen on anther monitor.
Please note that Actual Preview is not using cache. It will be slower but you'll get exactly what you get on export.