I'm a bit of a cave photography virgin myself, but have been playing with a sony digital cam. The nice thing about digital is you can check your results on the spot, but the downsides are a lack of control over your pics, unless you can afford the proper digital slr's that are appearing now.
Any on-camera flash will suffer badly from reflected fog from steam and breath, especially in small passages, so a detatchable flash or alternative lighting is a must. I can recommend having a read around the
uk cave photography group webpages.
Whatever you go for, I can thoroughly recommend a
Pelican "peli-case" to keep it in. These cases are fully watertight, float, and are tough as old boots.