Hi,
I have just encountered a problem in obtaining required spare parts for my compact camera housing so have decided that it's sensible to upgrade to an SLR-system rather than going for a new compact-camera setup. I have not had time to research all the options regarding camera specs and camera/housing combinations yet, however I would be very grateful if some of you would share your experiences and give me your views on the following:
What would be your recommendation regarding choice of camera (camera will be both for UW-use and for land-use; doing a fair bit of nature photography on land)? Good and bad points?
Recommendation for UW housing, incl advantages and disadvantages with the recommended housing?
Lens recommendations for someone new to SLR both UW (good macro set-up esential, but wide angle also of interrest) and on land (especially wrt nature photography).
I appreciate that it may be very difficult to answer with so little info from me, however I'm interrested in hearing what your choices would be.
Thank you in advance for sharing your knowledge!
First off is the question is what is your budget? That will be a big factor.
Second, if you are doing a fair bit of photography on land, what type of photography? Close up nature of bugs, landscapes, etc. For instance - whether AF and FPS is something you need. I love my 5D Mark II for many things, full frame, good low light images, but it does not focus as quickly as some of my other cameras or do the same FPS. When I am shooting trees, not a big deal, if I was shooting birds in flight, bigger deal 
The size, weight and ergonomics of the cameras are important. I prefer cameras with dial wheels that I can change Speed and Aperture with my index finger and thumb and as oppossed to others cameras where you need to press a button. The extra dials are generally on the more expensive cameras.
Have you shot an SLR or dSLR before (do you own lenses?) If you have glass that can influence things. Have you shot a friends dSLR?
The big players are Canon and Nikon and cameras range from $500-$600 to OH MY GOD prices.
This is a good list of brands, pricing and features, though there are others on the web of course
http://imaging-resource.com/MFR1.HTM
There are many brands of housings to choose from. In general, there are the plastic/polycarb housings (which tend to be less expensive) and aluminum/metal housings (which tend to be more expensive, but may function a bit better, be more streamlined and lighter.) In general order of cost, sort of, - Ikelite, Aquatica, Nauticam, Sea & Sea, Hugyfot, Seacam, Subal.
There are some general lens selections that many generally agree on. Usually people will have a Macro, a Telephoto, a prime or two, a walkaround lens. LOL. Glass can add up. If on a budget, even some of the kit lenses are okay (better than they were) and can get you started. Yes, not the same as buying other lenses, but can get you off the ground. Usually the incremental cost of adding the kit lens is worth it, maybe $100 more or so. I shot an 18-55mm on my Canon until I started glass collecting. Was fine to start with.
Easy, I'd get a Nikon N3 ...
What is a N3? Did you mean a D3?