Hi !
The air filter on the TDI is located below the engine.
To reach you have to get under the car and remove the protection
plate below the engine. When you have remowed this you will see the
filter housing. The filter itself is 25-30 cm long and app 15 cm in diameter (it's round) !
I have replaced mine with a K&N high flow filter !
Good luck
BK
2003 Silver 1.4 TDI 100 hp / 245 Nm S-Line (Sport) with Open Sky, ECC, APS, CruiseControl, Navigation Plus + TV + BOSE + CD changer, Sideguard, Mobile phone, El. rear windows, Fog lights, Winter Package, ISOFIX, Headlight washers, Space Floor, 17inch winter wheels, B&B Chip, K&N High-Flow filter, Webasto stationary heater +++++++ (KW adjustable suspension, Audi Styling kit etc to come)