How Do I Enable Wi-Fi Sync For My iPad?
First make sure you have iOS 5 installed on your iPad. Once that's squared away, plug the iPad into your computer and launch iTunes. Select your device in the iTunes sidebar, choose the Summary tab, and then enable "Sync over Wi-Fi connection". You can then disconnect the device from iTunes.
From then on, if your iPad is plugged in and connected to your Wi-Fi network it will sync with iTunes on your computer.
This works for both the iPhone and iPad.