If you need to resync, what you need to do is press the hidden SYNC button under the front flap of the Wii. Immediately after, press the sync button under the battery cover of your Wiimote.
The controller that comes with the console comes pre-synced (according to my source at Nintendo), while the others will need to be synced in a similar manner.
They use Bluetooth, so you have to do it this way so that they can exchange the keys properly.