Hi BigZ,
If you are refering to the addin keypad that Microsoft offers for the Controller, the answer is, it should work but I am not sure. As I understand it, the keypad is really just a USB keyboard that uses the XBox360 controller as a pathway for communication. If you hook up the keypad to the controller and it starts working like a keyboard, then it should work. Try it and let me know. If it gives you any error messages, let me know what they are. I might have to add the productId of the keypad, but I don't think so.
Lee