from snopes.com:
Origins: The photographs displayed above are genuine, but they don't quite depict an automobile "made from solid silver." The shiny appearance of the Audi A8 pictured here is not due to its being made of silver, but to a customization involving a special polishing technique used to produce a chrome-like finish, for which the car's Dubai owner engaged the firm Motoren Technik Mayer (MTM), based in Wettstetten, Germany.
http://www.snopes.com/photos/automobiles/silveraudi.asp
I wonder why people keep posting all the email chains they get in their inbox