I just ran across some awesome information on the http://www.wiili.org/index.php/Main_Page
wiki pages today. This wiki is primarily about using Wiimotes and Nunchuks with Linux, with a little info about PC and Mac OSes as well, but I followed a link there from one of the electronics blogs to this article about motion analysis of the Wiimote accelerometer and sensor bar data which had a lot of insight into how to integrate all of the data to get a full state of the controller and its position. If you combine this with the info on reading the raw data via the Arduino (linked above), you should be able to interpret almost anything you would want.
Motion Analysis: http://www.wiili.org/index.php/Motion_analysis