Shooter,
This page will give all the information you are looking for Trails, Clubs and ATV Rules.
There is a new 1,000 mile loop just open up North.
http://www.nhstateparks.org/experience/atving/
You are not going to find many areas in or around the Lakes area for ATVing.
My pet peeve here is that (some) of the DEALERS like selling ATV's but they do not want to tell you
where you can find a place to ride them.
Check this Website out and I think it will answer all your questions on local riding
NEW DURHAM VALLEY ATV CLUB
1 Jackson Lane, Center Barnstead, NH 03225
www.newdurhamvalleyatvclub.com
jwheels@metrocast.net