If you're connecting to a television with neither HDMI nor VGA inputs, you can instead use the $39 Apple Component AV Cable or the $39 Apple Composite AV Cable, as appropriate, although both offer lower resolution than the Digital AV and VGA adapters. Although this wired approach works just fine, it's difficult to hold your iPad while giving a presentation without the video cable falling out--I speak from personal experience.
Mirror a newer iPad With an iPad 2 or later, either the Digital AV or VGA adapter lets your iPad mirror everything from its internal screen onto the external display, which may be useful if you want your presentation to include demonstrations of other iPad apps or content that's not within Keynote itself. However, note that on the original iPad, where mirroring is unavailable, Keynote itself produces no external video signal until you tap the Play button (which is probably what you want anyway).
If you prefer to roam across the stage holding your iPad while you speak, you can beam your presentation's audio and video wirelessly using AirPlay mirroring--provided you have an iPad 2 or later running at least iOS 5. To pull off this trick, you'll need an AirPlay receiver connected to the projector or display and on the same Wi-Fi network as your iPad. Apple's $99 Apple TV ( Macworld rated 4 out of 5 mice ) can serve this purpose, if you happen to have one handy. Alternatively, assuming a Mac or PC is available, you can install either of two similar utilities: AirServer (Mac version, $15; Windows version, $8) or Squirrels' Reflection (Mac only, $15). Either of these apps can turn a computer into an AirPlay receiver, no Apple TV required. They even support displaying screens from multiple iOS devices at the same time. Note that the PC version of AirServer currently lacks audio support, but the developer says it's "coming soon."
Once your AirPlay receiver is set up, you can mirror your iPad's display by double-pressing the Home button, swiping the multitasking bar toward the right, and tapping the AirPlay button. Tap the name of the device you want to use for mirroring and then set the Mirroring switch to On.
(Image Caption: With an app like Reflections or AirServer running on your Mac, you can mirror your iPad's display and audio wirelessly.)
Control the presentation