There is no dive certification that I know of for depth limit.
What you are talking about is a 30 minute orientation to diving and then you go 1:1 with a dive master to a shallow reef. Itís great. That's how I started.
See PADI.com for information.
HINT: Stick the regulator in your mouth, inhale, if it works, stick your face in the water. If they see you are comfortable they may take you to a nicer place. Also, read about diving in magazines. Hint: Changing vertical direction is more about changing lung size than moving arms and legs. Also, get horizontal and pull your weight belt up a bit so itís not hanging on your hips so you have an easier time keeping horizontal and ďthe finís upĒ