If in doubt consult Emmanuel! The Owners Manual 3.1 (controls and equipment) Page 33 -Locking- states that if you use the key in the driver's door and turn it twice it will lock the car in the 'Safe Mode' so that the interior door locks remain unlocked and the alarm remains off, and the deadlock red LED remains off.
All versions of the TDI have timing belts which need to be changed at the recommended intervals (Iwould worry over 60,000miles or 6years; and over 80,000 and 8 yrs I would tow it to the garage!) Find out the engine code for your car - you will need it for spares and consumables - mine is AFN (110bhp built 1999) with the old style rotary pump with No 3 injector with a sensor (just a magnetic search coil) to tell the engine management computer when the needle lifts and starts spraying.
Yours might be the AJM or AJT version with the unit injectors which is more expensive to produce and maintain but gives amazing torque and is more economical.
I would highly recommend the car generally but take time out to learn the systems, and beware you do not get locked out. It is almost impossible to get back in without seriuos expenditure. Keep a spare uncoded key outside the car just to get in, and a further normal key looped on a piece of string under a seat or locker to start the engine. I have already locked myself out twice and had my keys stolen in just 6 years.