This is actually a good time of year to start a basic open water (OW) class. Start with a local dive shop (LDS), see what they are offering. As SCG said above, Aquatic Specialties, if you're local to that area.
There are numerous certification agencies, the most prominent of which are NAUI, PADI and SSI. Ask ten divers, and you'll get ten opinions as to the best certification agency, but I am very biased toward NAUI for reasons I will not get into here. Bottom line: It's the instructor that makes all the difference. I've been very lucky, having taken my certs from divers including a Navy Diver and a crew member from one of the top Jersey wreck charters.
For a basic OW class, you can expect a series of classroom sessions (say, 8-10) hours, followed by 8-10 hours of pool work. At the end, you'll have to do a series of required open water dives in a lake, quarry, or ocean. In each of these, you'll be required to demonstrate a specific set of skills. The best thing to do after getting the OW certification is to get a few dives in your log and then get your advanced certification, which includes some electives such night diving, deep diving, navigation skills, etc. I am also a big advocate of the equipment specialist certifications, which provides you with a better understanding of *how* the equipment works, and enables you to troubleshoot problems.
As mentioned above, the folks at Dive Winnipesaukee run charters on the Lake, and also offer classes. It's the best of both worlds -- diving AND being at the Lake.
Check out the NAUI site for some class descriptions:
http://www.nauiworldwide.com/index-side.html
My favorite Web resource for all things dive-related:
http://www.scubaboard.com
Dive Winnipesaukee:
http://www.divewinnipesaukee.com/
Hope you pursue it. If, as a kid, you ever wanted to fly or be an astronaut, or if you sat and religiously watched Jacques Cousteau specials, then you owe it to yourself. And Winnipesaukee is a wonderful place to enjoy diving.