I've adapted a iMac 24" Aluminium InfraRed Sensor Board (part #820-2151) to be used on my desktop hack
The cable I used was from a G5 case temp sensor (the small 4 pin connector is the same). In the other of the cable end I trimed the connector to fit into a internal USB header. The pinout is as follow (pin 1 is the one marked with a 'v' printed on the board):
Pin 1 - data-
Pin 2 - data+
Pin 3 - 5V
Pin 4 - GND
So is recognized natively and works perfect with the Apple Remote Control...