VAG-COM is a software program for a PC that converts the PC into a factory level
diagnostic tool for all electronic diagnostic capable modules in VW/Audi/Seat/Skoda cars. You need a PC and you need an interface from the PC to the DLC port on the car. This port is a standard 16pin connector that is in all cars after 1995 to permit emissions related diagnostics. The OEMs chose to add full diagnostic capability through this diagnostic port.
VAG-COM, now called VCDS, allows the user to scan all modules for Diagnostic Trouble Codes (DTCs commonly referred to as fault codes), measure live data, code modules, perform basic tests and settings, perform adaptations and so on. The full version of the tool provides the same functions as the VW factory tool but costs 1/20 of the price of the factory tool.
As to where you get one, the advice given by andycupra is good advice. Look around the forum. If you want the real deal from the manufacturer, then visit the Ross-Tech web site (
www.Ross-Tech.com) and note our distributors.
Merry Christmas and Happy New Year