I bought my BMW (E46) 318IA brand new in March 1999. Till now, it is 6 years 10 months old. The air conditioning system had no problem at all.
Over the years, the repairing was not too much. I think the amount of repairing depends on how you keep and use your car. I always park in covered car park and drive the car carefully.
I think the technology and workmanship from E36 (ended in 1998) to E46 (just ended in 2005) had improved a lot. I always heard people said E36 had a lot of problems but my E46 did not had much problem. May be my car had low mileage (6 years 10 months 57,000 KM).
I used to drive a E46 for 3 years not with even one problem, but I am only a weekend driver with very low mileage! I would highly recommend 3 series from year 2000 onwards.. Good and reliable car
But the older model, I heard lots of bad things, like electrical problem !