I'd urge you to seriously reconsider starting UW photography as a beginner diver. You need excellent dive skills to even have a hope of safely pursuing photography UW. Its surprisingly difficult compared to shooting on land.
Please spend some time diving first before trying to shoot photos. I cannot stress this enough.
That being said, there's also a huge difference between shooting with an big heavy SLR rig and a small point-n-shoot camera. SLR rigs are very awkward to handle in the water - all it would do as a beginner diver is to make diving much more frustrating and dangerous to you and your buddies.