I've got the DSC-P5 and have been using it for a 2 years, 3000 pictures later.
The settings I use underwater are as follows. Flash forced On, Low power setting (not what you would guess, any other setting is just to hot), Wide angle (always, forget the zoom underwater), Macro Mode On (if it's out of range of the macro it's to far away), ASA setting I've been using Auto but really think 200 or 400 is the right answer, and everything else Auto. Resist the urge to play with the sharpness, it will increase the contrast, but if overdone will kill the picture.
On the battery life, Keep the Power Save On, I was able to get two dives on one battery but it was a challenge. I would switch on the camera, take a picture and turn it back off, this will also minimize fogging. It will charge back up pretty quickly, maybe a hour or two. Be very, very carefull about sealing the case, two big issues, the shape of the o-ring (needs to be very clean, remember one hair or spec of sand and your camera's toast), and the humidity when you seal it. You want very dry air in your camera case anything else and it will fog. A carefull cleaning of the inside of the case will help this also. If it does fog you will not get any pictures till you dry it.
Have you thought about how you are going to attach the camera. It is slightly negative undeerwater, I have a nightmare of watching my camera dissappearing into the deep blue. What I use is a coiled lanyard clipped to my BC. When I get in or out of the water the caerma goes in a BC pocket for protection, once at depth, out of the pocket, unclip the lanyard and I can hold the camera at arms length. If not in use under a BC strap.
The other advice is learn everything you can about the camera before you go underwater. You don't want to be going up the learning curve of the camera while swimming in rip current with hammerheads. Shot anything that moves and alot of stuff that doesn't, right now. Remember it's digital and pictures are free. Learn how to switch Macro Off and On quickly. The other feature that is very handy, last picture preview. If your looking at the last picture, hit the zoom button and you can zoom in to check the focus. If not in focus shoot another.
Best of luck and we want to see the results.
