Clinton Blackmore form the Southern Alberta Robotics Enthusiasts club put together some pretty neat software to control Lego NXT motors and sensors by using the Arduino microcontroller.
Lego NXT robot Controlled by Arduino
As shown in the video below, he is using the Mindsesors Multiplexer for NXT
This is a companion discussion topic for the original entry at https://community.robotshop.com/blog/show/lego-mindstorm-nxt-controlled-with-arduino