Don't forget there are underwater digital cameras that do not require a housing. Olympus makes several. I have the Olympus Stylus 1050 SW (10') and Olympus Stylus 1030 SW (33').
If you already have a digital camera that you can get a housing for, it makes sense money wise to go that route.
Another option is to rent a camera while there but this might be expensive, however the camera quality is much better.
I have only used mine snorkeling and must admit, as Harriette says, you need practice taking underwater pictures.
Look forward to seeing the pictures.