From Ross-Tech Wiki
3.1 Do I need an Interface Adapter?
Yes. The ISO-9141 port in your car is not directly compatible with any standard PC port. The ISO-9141 port in your car is somewhat RS-232 like, but you can't just wire up a cable -- you must put electronics in between to allow a PC to communicate with the car. We offer several complete packages consisting of an Interface Adapter, the full-function version of VAG-COM, free updates and unlimited tech support starting at $229.
