Where is the thermostat located on a 1998 VW Passat?

It is mounted inside the water pump assembly which is essentially buried in the front of the engine. When I recently replaced my timing belt I also changed my entire water pump including the thermostat, just in case. Be aware that this is an entire day job for a do-it-yourselfer. I would suggest also changing the timing belt as you will be pretty much ripping apart the entire front end of your car to get to the waterpump. Go to http://www.clubb5.com and check the forums. There is a forum called "Garage" that has a complete write-up of this procedure.