Mac OS X Tiger/System Preferences/Displays
This window allows you control over aspects over the monitors connected to the Macintosh. You can choose the resolution, the number of maximum colors to display, and the refresh rate. The Detect Displays button flashes a number on each monitor if you have more than one monitor installed, while the Rotate button allows you to rotate the monitor 90, 180 or 270 degrees. The Rotate button is only present if you have a video card that will handle screen rotation.