I'm not familiar with the D200 but the greatest aid to focussing I ever found was to map focussing to the AE/AF lock button... CSM menu AE-L/AF-L = AF.
Then set CSM menu Autofocus = AFC.
What happens is that you use your thumb to focus with the AE/AF button and just meter with the shutter button - no half pressing nonsense - I shoot from the back of a bike and half pressing doesn't work.
With the thumb it's much easier to track things and if you find a bird sat on a tree you thumb press once, release, any further shots will already be in focus as the shutter button doesn't engage focus.