You do not need a special license to operate an ATV in New Hampshire. Although, you must register your vehicle. You will not be permitted tooperate an off-highway vehicle if your driver's license is under suspension or revocation in any state or Canadian Province. If you are crossing apublic way, you will need a valid driver's license or an OHRV Safety Education Certificate.
Check out these Suncook, NH ATV/OHV resources: