From a former newbie to a few others, I suggest starting out with a G9 or something similar (high-end P&S with RAW and manual options), instead going straight to a DSLR. I started 5 years ago with a little Canon A80, had a lot of fun with it but wanted more, and so moved on to a 20D and Ikelite housing and strobes a few years later. After two trips with the larger, snazzier more-difficult setup, I'm now looking to downgrade my underwater kit to the new Canon SX1 or maybe a G10, while maybe upgrading to a 5DMkII on land... if don't lose my day job.
Why? The DSLR set-up was heavier, more complicated, and more expensive than what I really needed as a novice photographer who doesn't dive often for big-ticket set-ups to be sensible for me. I spent way too much time on my honeymoon in Bali fiddling with the multiple o-rings, settings, ports, battery chargers, and on. And when I went to Tonga, there was similar imbalance between taking care of the u/w set-up and revisiting this weird, beautiful place where I'd spent two years of my early twenties. Unless you're willing and able to take the time to really make the most of a DSLR set-up, it's probably better—and certainly less expensive—to start with something smaller and a little bit less powerful.
Just getting a DSLR body and a few good u/w lenses will set you back $1200, at least. Add in the housing, strobes, ports, etc., and you can easily drop another two grand. (And that's before true "gear lust" kicks in, which will make you buy neat things even if you don't really need them.) Also, the chance of flooding a housing means, to many of us, that it's good to have a second camera as a backup… so that's another $500-$1500, easily. If you don't dive that much, that's a lot of money to be spending.
Just my two cents.
-Dan