timing belt change intervals

How often are they supposed to be changed? The car is an 87 Jetta freebie that my friend just inherited. She took it to a mechanic who of course recommended $800 for a belt and water pump. I can do it in an afternoon for her, but I wanted to know if it needs to be done or if he was just trying to line his pockets.

I'd get a new mechanic. I changed the timing belt and water pump in about an hour. Parts are about $100 if you buy them online. You have to remove the Alternator, A/C compressor (don't detach hoses - just set it aside) and power steering pump to access everthing. Setting the timing isn't difficult. Get a Haynes or Chilton manual. As far a tools are concerned, a decent metric socket set and a universal socket adapter are about all you need. You'll need allen wrenches (sockets are better) and screw drivers. The job is pretty easy.