glbtrekker, congratulations on signing up for your course! It sounds like a good one -- meeting twice a week for an entire month should give you lots of time to get comfortable with your equipment and your skills. I should think that May in TN would be a lovely time to be outdoors and on the water, not too hot and not too cold. You should have a great time!
Do get the administrative issues sorted out, so that you are sure you will get a C-card at the end of your class. I'd talk to the owner of the shop and ask him whether you will be using NAUI or PADI materials for the class. If you are using NAUI materials, you should get a NAUI card. It doesn't really matter which card you get, as far as your ability to go diving anywhere, but it just says the shop is following procedures and not bending rules or using shortcuts.
But the important thing is that you are going to learn to dive! Come back and tell us how your class goes.