If you'll do a search on the topic of beginning cameras you'll find lots of info.
You're first decision has to be a budget. What are your spending limits? You can get affordable digital and film cameras for just a few hundred dollars. Then decide on the purpose of your photos. Do you want to print them for photo albums to show your friends, want enlargements? What size? Want them mainly to send in emails and share on the web? All these answers will lead you a bit further to a camera that will suit your needs.
Film cameras may be cheaper to start out but you'll have the expense of film and processing, limited number of shots, fixed focus. Unless you have the money and desire to go with a housed SLR, I think you'll be better of starting with a digital.
Digital may cost a bit more to start but you'll have a memory card to use over and over again, you have instant access to view your photos to see how you're doing. This gives you the chance to re-take some photos. Fish don't always wait around! Depending on the quality you choose, you can take hundreds of shot on a single dive, the auto focus and zoom lens make taking photos so much easier. Digital cameras also handle low light better than film cameras, making an external strobe unneccessary to start out. I think the learning curve on digitals are smoother than with film cameras.
I'm a fan of Olympus digital cameras and housings but that's becasue I have one! Cannon also haas an excellent line in their S-3XX and S-4XX cameras and housings. I would suggest no less than a 3 megapixel camera. It can still make decent 8x10 enlargements with the right compression and are reasonable priced.
