Personally, I wouldn't take a D200 underwater unless you have had years of underwater photography experience. It's the cost, the equipment and the challenge of handling complex dslr equipments under water, etc etc that makes it really challenging and if it's a D200 setup, chance of loosing that setup because of flooding is very high due to being a beginer.

Having said that, a good point and shoot with an excellent single strobe (like an Inon or Ikelite) might be a choice of learning underwater photography. They can take outstanding quality pictures.

I have recently switched to shoot dSLR after my beloved Olympus C5050 point and shoot and so far I have achived no pictures from my Nikon D80 that is any better then shot with the Olympus. I think by the end of this year, things should change but meanwhile, it's a learning curve.