I might know this one! First, give your model a bone in 3DS. Then skin your model to that bone. Then animate the bone rotating as you desire. Finally, when you export, make sure to tell it to export with animation. Nif files can contain (at least one) animation(s). I know that the logo.nif also has a flag that tells it to autostart just incase your nif's animations don't start on their own.