So here's the quick answer and then a long one.
Quick: Grab a housing for your camera (especially if it's point & shoot). You've got to be comfortable with controlling the features. Next, buy a very good strobe and be prepared to spend money on it. I'd recommend any of the higher-end Ikelites or Sea & Seas. Your lighting is more important than your camera. Most amateurs come out w/very blue pictures or over-exposed pictures w/flash. Putting money into the flash allows you to upgrade your equipment (which most people do if they get into it) and you don't have to junk your investment in the flash.
Long Answer:
Most new photographers take cheap down and it shows. I did. I had a Nikon point & shoot (a high-end one though) and a Fantasea strobe. Well over 2/3rds of my pictures were throw aways. All of my pics had 2 common issues - blurred or incorrect lighting. The blurring was caused by inadequate shutter speed and auto-focus speed from the camera. Most P&Ss are great for still pictures and when you have time to setup. Neither of these happen underwater frequently. The 2nd issue was bad exposures (over or under or just blue water). That was a weakness in the strobe. Most cheaper strobes don't throw off alot of light and the angle of the light is relatively narrow. Combine that with the fact the strobe isn't metered to the camera (they fire when the camera flash fires and fire the same light regardless of what's needed), and you can see the dilema. That means trial & error shooting until you get what you want.
So here's the reason for all of this. If you get into shooting underwater, you will upgrade. To what will depend on your shooting. So before investing a ton, go shoot. See what you like and don't like. Then you can be specific on your needs and your budget (underwater photography can cost a small fortune). If you've got a good strobe, you're going to immediately increase your odds of better pictures (since color loss is the main issue) and you've got an upgrade path.
I now shoot an SLR with dual strobes. On my last trip to Bonaire, about 80% of my pictures were keepers and I have several that will be in competitions this year. The bad ones were because of me, not my gear. My old Nikon setup is sitting in the closet - I use it when instructing UW photography. My cheap fantasea strobe - I sold it for 30 cents on the dollar to a friend just starting out (after I bought it new a year ealier). On my Bonaire trip in December, there were about 15 photographers in our group. As I expected, the ones with the better flashes and gear (yes these were more expensive) had the better pictures (and they had a higher percentage of keepers).
One of the rigs I saw that I liked was a Canon G10 with a single Ikelite DS51. Two of the advanced photographers (one owns his own studio) were shooting this setup. Neither matched my SLR, but they both came away with great pictures. The setup still has some of the inherent issues with focus, speed, and light metering, but the camera was very fast relative to most point and shoots, and the strobe more forgiving.
If you want to see pictures, contact me and I'll be happy to share to show you what I'm talking about.
But it does the job for "memories".
