Here's a place that carries the Ikelite housing for the Rebel 35mm SLR, and
here's a super-duper kit with a stobe.
I'd have to say that I considered the film option before I started, and I'm glad I went with digital
in the long run. Film may force you to "know your camera" a lot better and "adjust properly" for the best shot. I was just content with snapping a bunch of shots using different settings and using what worked...and I still have room left for more pictures. Try to change your film underwater.
Ok...so...I'm a little bias to digital because of my background, but I guess it really depends on what you want to do with the camera. For the price of that second setup I linked you to with the strobe, you could get a Olympus C-5050, PT-015,
and a nice YS-90DX strobe and tray/arm to go with it. Now all you need is memory (and maybe a wide-angle lens) and you're set. That previous setup
doesn't even include the camera.
Oh well, like I said, I'm a little bias. Digital seems just so much easier to learn on.
Ok...I'm done.