You can play your Keynote slideshow on various kinds of projectors and external displays.
If you have a choice between a DVI connector and a VGA connector, use a DVI connector to connect the projector. DVI connections generally result in the best image quality and are easier to set up.
Set the native screen resolution (the size of the image on the screen) in the Displays pane of System Preferences. Look for this information in the documentation that came with the display. For most projectors, the preferred screen resolution is 800 x 600 or 1024 x 768. Most liquid-crystal display (LCD) and Digital Light Processing (DLP) screens work with a variety of resolutions, but one is the preferred setting.
To change your computer’s screen resolution, choose Apple menu > System Preferences, click Displays, click Display, and then select the resolution you want from the Resolutions list.
Set the screen refresh rate (the number of times per second that images are updated on your screen) in the Displays pane of System Preferences. If you use an LCD display, LCD projector, or DLP projector, try to match the refresh rate of your computer or video card with the optimal refresh rate of the display device. (Usually this is an issue only if you’re using a VGA-style connection to an LCD or DLP display. CRT devices do not typically have one optimal refresh rate.)
If the colors on your display seem “washed out” when you connect to a new projector or if the text appears jagged, you may need to calibrate your display. Open ColorSync Utility (in the Utilities folder in the Applications folder on your hard disk) to set up color calibration.
If you’re set up to use a dual-display configuration and you want to switch the Presenter Display to the other screen during your slideshow, press X to toggle the displays.