DS is 16 months, and we will be starting a mommy/me swimming class next month which I am really looking forward to, there are no floaties allowed . You should really check out the Water Babies way of teaching swimming from infancy. I believe they have DVDs you can order.
Since DS was a baby we have put him underwater. Now that he is older/aware we can't do it as easily anymore, so we are teaching him to blow bubbles, an essential step. We can now submerge his mouth for a moment, and he does not suck in water. But he does loooooooove, the water.