PS-I know you mentioned you may not have time to get scuba certification. I used to teach, it takes at least a full weekend to go through all the classroom modules and pool exercises, but that's for certification.
There is a course that is offered at most resorts around the world that is designed to be a "discovery" session. It involves a few hours poolside going over the basics, followed by a supervised shallow dive. Ask about it at a local dive shop in Belize.
Here's the "Discover Scuba" course.
http://www.padi.com/scuba/padi-cours...g/default.aspx