I have done the rent a drum sander/edge sander route, and since it was a long room and I was a novice, the results were a little less than stellar. I ended up with an improvement, but there were little dips. I recently saw what amounts to a huge walk benind version of palm sander on one of the home improvement shows. That type of machine looks like it would be a lot easier to keep the floor level. Ignore this if the floor has gouges or dents because it doesn't remove wood fast enough to be practical for that.