TKJ Electronics has released a LEGO NXT Servo Motor
shield for the Arduino
. This shield can interface with up to two NXT motors as well as the ultrasonic rangefinder. In addition to controlling motor speeds via pulse-width modulation, the shield reads the motor’s encoders so that it knows the position of the motor with a precision of 1 degree.

The NXT Motor Shield is discussed in the TJK Electronics Blog.
The NXT Motor Shield kit can be purchased at the TJK Electronics Store.

Extra NXT motors and Arduino units can be found here: