As greg said VW says 105K. There is a greater chance of making it to 105K than a premature failure. However there are enough cases of premature failure that it can be justified to do it aorund 60-70K.
The premature failures are not typically the belt, but one of the components, liek the tensioner. All in all if your car has been regularly maintained and inspected by a qualified professional you should be able to make it to 105K.
Usually once a car is out of warranty or free service owners tend to stop going to the dealer for service and eitheer maintain it themselves or through an independent mechanic. This can cause oversight in some maintenance aspects that could help lead to this premature failure.
You can probably do the timing belt yourself. A few places like ECS Tuning sell kits. They usually include the belt, tensioner, rollers, water pump and t-stat. A few years ago it was done on 6 B5s in one day
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