As nigel stated, you have to watch the model years. When I was looking for my car, I saw a number of people advertising TDIs from the early 90s. When I called some up, they didn't know there were different engine models, and figured if the newer diesels were TDIs, then the old ones were as well.
Passats were out in 1996 and 1997 with the TDI engine. It was then discontinued in the Passat and transfered to the Jetta ONLY (Golfs remained IDI). These were from 1997 to mid 1999 when the newer style VWs came out.
If you cannot do repairs yourself, VWs can be expensive to maintain, and the diesels even more expensive. As for being over 200000 kms, as long as the car was reasonably taken care of, there shouldn't be any big problems. Just normal stuff. Susp, brakes, tires, etc. Just be sure that the timing belt was done, and that should be about the main thing.
The IDIs apparently had some pully bolt issue where one bolt would come loose and cause interference causing the belt to snap or something, and some engine damage to occur. It isn't something which happened with every one, but it did happen. There is a fix out there, and if you need it, I can point you in the right direction.