Some time ago I described how to put presentations on a projector with a Linux notebook with two X displays. In the meantime, I have switched to a Dell D800 with NVIDIA TwinView. I still do presentations where I want the image from the projector in a window on the LCD, without showing my whole desktop. Here's how to do it.

After setting the TwinView parameters in xorg.conf, configure VNC's ~/.vnc/xstartup to start the Metacity window manager and a gnome-terminal.

All you need then is the present script to start the VNC server and clients. Drag the view-only VNC window to the right, adjust its position so the title bar is not visible (Alt + left mouse button), and you can start your presentation in the second VNC window. To use Firefox, you either need to quit it on your primary display, or start it as a different user.

When you are done, stop the VNC server with the present-kill script.