Originally posted by tinksdad
Weeellll,
The main difference is equipment and the necessary training. Scuba, is as your instructor will tell you, is a "equipment intensive" sport. The best approach would be to find a local dive store (LDS, there that term again LOL) and chat with them about the parameters of their classes. There are several organizations that teach. PADI, SSI, NAUI, YMCA, IDI, etc. The organization is not as important as your instructor. Find someone that will take the necessary time to teach you all the basic skills and will engage in some buoyancy training as well. The training usually lasts approximately 6-7 four hour classes with two days of open water training to certify. With you being in the Chicago area, the weather will play a factor in the OW part, especially if you want to get certified prior to the cruise. (I say GO for it!)
There is quite a bit of information about the complications of pressure and breathing compressed air underwater. You need to go through the training to understand how to handle these issues.
Several shops offer a try scuba class that will let you try the equipment underwater at a pool to see if it would be an interest to you, or (this wouldn't not work for the cruise) you could try a Resort course which teaches you the basics, but restricts you to dive ONLY with a instructor or Dive Master.
There are some that can't or won't do what is required, but once you see the miracle of the underwater world, you will be hooked!!
hope that helped.