Here's a link to some information we figured out. http://www.alandsuejohnson.com/digital_photo_discussion.htm
The last one we used was a Nikon S51c with a www.fantasea.com
case. I was pleased. You can see the pictures on the 2008 Ambergris Caye visit on our Belize page.
What you get doing it this way is decent snorkeling pictures and a camera you can walk around with. Probably not a great camera but decent snapshots. Fantasea makes cases for several of the Nikon cameras.