When you use a laptop to display a presentation, the screen of the laptop will be too small to be viewed by many people simultaneously, so you will likely want to use an external screen. Connecting an external monitor to a laptop turns that laptop into a dual-display computer--that is, screen real estate extends across both screens. To allow those watching the external monitor to see what you do, you need to set Windows up to mirror the two displays. Configure a Windows XP computer to mirror monitors when you would like both displays to show the same thing simultaneously.
Connect the second display to the computer while it is turned off. Turn the computer on and allow Windows to load.
Right-click an open area of the desktop, and click "Properties." This brings up the display properties for your system.
Click the "Settings" tab.
Remove the check from the box labelled "Extend my Windows desktop onto this monitor."
Click "OK." The second monitor will immediately begin to display exactly what is shown on the primary monitor.