Paul asked about what camera I was using for my underwater photos. It's funny that you asked on the day that you did, I had just been looking for underwater housings for the D300. I'm planning on upgrading to full frame this summer so the housing is going to have to wait until at least this winter and maybe even next year. They ain't cheap! Once I have the FX camera and a few lens then I will start saving again for the underwater housing and the Nikon D300 will become my underwater camera and backup.
But until then, I am using an Olympus FE-360 8mp point and shoot. It was rated in 2010 by one of the underwater photography magazines as the top underwater camera priced under $200. The camera has two specific settings just for underwater shooting that make adjustments for being underwater.
Olympus makes their own underwater housing for the camera that is rated to 160 feet I think. I know it's rated a lot deeper than I will ever go.
The housing lets you operate every function of the camera while underwater with separate buttons for everything. You can zoom in or out or use the flash, etc. with just the push of a button.
I also purchased a "Fantasea" Big Eye lens for the housing. This is pretty much a wide angle lens that is designed to use the water to help increase the angle of view. The lens attaches to the front of the housing and can be put on or removed while underwater. The lens requires that the space between the housing and the "big eye" be filled with water to work properly.
If you can hold still enough underwater the camera rig takes pretty good pictures.