It's not that the D3000 doesn't have AF, it just doesn't have an autofocus motor built in to the body itself. Originally Nikon started out doing AF where the lenses had no motor and the body had a little screwdriver thing that powered the focusing. They've since gone to in-lens motors which they call AF-S. The lower end cameras no longer include the body AF motor so they can't autofocus the older lenses that don't have motors.