DSLR OR P&S

I'm new to Underwater Photography and planning to setup my existing camera w/ an ikelite housing and strobe. Currently I have Canon 5D, Rebel Xt and S80(P&S). What camera do you think to setup? How difficult to take a underwater picture comparing dslr & p&s.........p&s you just view the LCD and take picture? How long can you master taking picture through the view finder

P&S is really point, shoot and wait. A DSLR takes the picture within a moment of pressing the shutter release. I found it difficult to take spontaneous pictures of my kids with my P&S!

Housing the 5D would be the best option.

I think it is better to grow into your system than grow out of it.

I second Peter's recommendation. It will also cost you more to upgrade in the long run when compared to starting with the 5D from day 1.