How can I use a Wii remote as a remote control for Keynote on my mid-2011 MacBook Air?
I believe that you'll need to download Darwiin Remote form here: http://sourceforge.net/projects/darwiin-remote/. This software will allow communication between the Wii Remote and your computer.

I haven't played with this for a long time, but I believe that when I did this app allows the Wii Remote to act as your mouse and provide direct interaction with the system (I used a candle to provide the required infrared source for tracking).