Enter the VIN/Chassis number of your Volkswagen into the VIN box at the top, tab out of the field and the information about it will be displayed below. It should work for most VW cars with a 17 digit VIN code (built after 1980) and those with a 9- or 10-digit VIN built after 1965. The information encoded in the VIN between 1965 and 1980 is much more limited, though.
The data behind it was gathered from the rec.autos.vw FAQ and elsewhere on the web, so it may not be entirely accurate and/or with info missing in some cases. If you have any corrections, please let me know.