Nedjosoft PpcObd is a Pocket PC tool which makes it possible to talk to your car by means of the OBD II connector. You also need a simple signal converter made of a microcontroller (Atmel's ATtiny2313) and a few other components. The schematics and the microcontroller firmware will be provided as well. The communication is achieved through the infrared port of your (old) Pocket PC.

There will be more info soon.