I looked at connecting the Wii Nunchuk to GH via an Arduino and have attached a working test example. The joystick moves a box in the XY-Plane and the accelerometer varies the XYZ dims of the box and changes the XYZ offset of a sphere relative to the latter. The C and Z buttons toggle the objects surfaces from translucent to opaque. The novelty wears off after about half a minute so I leave it to others to do something intelligent with the interface.
Nunchuk :-
Double-sided PCB board 1.6mm(1/16") thick is used for slotting into the connector.
Wiring configuration can be found at
http://wiire.org/Wii/protocols/wiimote_bus
the connections need to be mirrored for the Nunchuk - and
http://todbot.com/blog/2008/02/18/wiichuck-wii-nunchuck-adapter-ava...
analog pins 2 and 3 have been re-configured for power/ground - I've kept to the standard setup leaving the pins free for other inputs
Arduino (NG + v0017) :-
The code is adapted from
http://www.windmeadow.com/node/42
I've simply re-formatted the serial output to provide a consistent 20-digit 'number'. Regarding notes on altering the twi.h file I just uncommented #define ATEMEGA8 and left #define TWI_FREQ 100000L as is - my setup didn't work with the higher speed recommended.
GH (0.6.0019)
I've included the serial port code in the C# component by adding the System.dll referenced assembly from from my C:\WINDOWS\Microsoft.NET\Framework\ directory - the namespace already exists in the component but didn't seem to recognise the functions.