http://letsmakerobots.com/node/5712
http://todbot.com/blog/2008/02/18/wiichuck-wii-nunchuck-adapter-available/
There's an example at the bottom of the page.
I haven't played with the nunchuck so I can't say if it works or not.. but I know a common mistake is if you're using a mega, or a Seeeduino board, the Wii Nunchuck Adapter from Todbot won't work without some modification.. generally using a bread board or something.
Do let us know how you get along, and what your mistake was if you found it, I do plan on getting one of these bad boys soon! (they're $6.99 with free shipping on eBay, how can you say no to that?)
Hope this helps! (I hope I didn't shoot and miss and read over something important, :))