For Tenessee:
http://www.tennessee.gov/revenue/vehicle/index.htm
http://www.tennessee.gov/revenue/veh...ortedmoped.htm
The second link states you need an HS-7, don't worry about it, apparently it's something the manufaturer and the state works out. You will need the bill of sale and MSO/MCO, without them no tags or registration! Nothing needs to be Notorized though, TN did away with that several years ago.
Also, for most of Tennessee, you can plate a dirt bike, you need a headlight and a tail/stop light. Turn signals and horn are optional. The larger metro areas like Memphis and Nashville are more strict and I think they have inspections and I think have their own requirements.