Finally, Microsoft has changed the way Windows detects and handles external monitors and display devices (including projectors).
In Windows 7, you will be able to press the Windows Key 
+ P (or type ‘displayswitch’ in the ‘Start’ menu and press enter) in order to bring up a menu which includes the ability to display:
• only on the local monitor;
• only on the external monitor;
• have the same content on both the local and external; or
• have separate content on both (ideal for using PowerPoint Presenter View)
Windows 7: Display Projection