My first suggestion with most "losing coolant" situations is to get a pressure tester (you can usually borrow them from Autozone and similar places). If the leak is external, you will usually find it.
On my '98, it was using coolant slowly when I first got it. I put the pressure tester on it and let it sit for several minutes, then I could hear the tell-tale drip off the engine. The leak was slow enough that the coolant would evaporate away instead of dripping on a hot engine. With the pressure tester on a cold engine, I was able to track the leak to a spot on the intake gasket (intake gaskets are a common complaint on these engines).
That's where I'd start.