Mac OS X 10.6: Setting up multiple displays as an extended desktop
If your computer is connected to more than one display or to a TV or projector, you can set them up as a continuous display for your desktop.
To set up multiple displays as an extended desktop:
Connect the displays to your computer.
Open System Preferences, click Displays, and then click Arrangement.
Follow the onscreen instructions.
You can also show the same image on all the displays connected to your computer. This is called “video mirroring.”
If your computer is connected to more than two displays, you can specify that some are mirrored displays and others show the extended desktop. For example, if you have three displays, you can have two displays showing the same information and the third display showing the extended desktop. To set up a combination of displays showing mirrored and extended desktop images, set up the three displays as an extended desktop, and then Option-drag a display icon onto another display icon to mirror the two displays.
If you are playing a DVD on a television connected to your computer, click the Arrangement button in Displays preferences and move the menu bar to the television. If you don’t see an Arrangement button, your computer is only capable of mirroring (showing the same image on all screens). For more information, see the manual that came with your computer.