also, while you're at it, get the d3 too, and the d300, and the d700, the more the merrier
jokes aside, please indicate what your priorities are, what you want out of a camera, and what you perceive is the difference between the two cameras.
if you can answer these, you will know which to pick. or do you want others to do your homework for you? in which case others will end up pushing their own personal choices at you, and you won't get an answer anyways.
As the others have mentioned, it largely depends on what your needs are.
The one thing that the D200 have over the D90 is its built quality. Personally, I prefer the handling of it more than the D90.
Other than that, the D90 has better ISO performance, latest GUI and also a larger LCD. It's also a lighter body, which some might prefer.
If you're just starting out, the D90 might be a better choice for you. Unless, you want the better build and the ability to meter with the older Nikon lenses. Not sure if you can get a D200 brand new nowadays, but the price would probably be close to a D90 body.
in my opinion, i think you should get the d90. Noise control is by far a much more important aspect then grip etc. If you've got inherent noise in your pictures, even if you do loads of Ps, its still not going to be that fantastic.