Re: hard starting 99 Jetta tdi
1) Does it turn over quickly or slowly? In other words, how's the battery?
2) Does it smoke badly when it starts?
If so, this could be (I guess at least) two things: The anti shudder valve may be sticking (this is on the intake manifold, toward the back/top of the engine). You can open/close this valve by hand, and you can tell if it's sticky. Search the forums for anti-shudder or anti shudder and you'll see some info.
It could also be a timing belt that's hanging together by threads and is way out of wack. Check that asap and don't drive the car until you're sure the timing belt is OK.
How does it run after it starts?