we just pulled up our carpet and our hardwood floors underneath look fabulous! i want to put a polyurethane coat on it. do i really need to sand down the floors first? if i do need to sand them, do i have to rent a machine, or can i do it by hand (the room isn't too terribly large...11x14 or something like that). what will happen if i don't sand the floors down (if i am suppose to)? thanks!!