Wood – Sanding screen vs Sandpaper for hardwood floor

Yes! Cleats are pretty much the standard in hardwood flooring. Typically, hardwood floors have 'tongue & groove' joints that interlock. First, some definitions of terms that I've used in my answer:

Tongue: the part that sticks out of the hardwood piece is called the 'tongue'.

Groove: the slot it fits into is the 'groove'.

Face: the part of the piece that will eventually be the floor is called the 'face'.

Floor joists: these are horizontal panels that run from one end of the room to the other and rest on beams under them. These provide support and you'll install the flooring on the joists, perpendicular to the direction in which they run.

CLEATS

With cleats, you drive the nail through the tongue onto the floor joists at a 45 degree angle. The cleats (which need to be set in) get hidden by the next piece that overlaps the previous one. The advantage is that all except the last piece in the room will have no nail markings on the surface.

The only con is that you'll need a specialized hardwood floor nailer, that can be pretty expensive to buy ($400-500 for a pneumatic one and $200-300 for a manual one). Needless to say, the pneumatic one is less work (but then again, you'll need to get a compressor for it) than the manual (you'll need a 5lbs mallet to drive a 1.5"-2" cleat in fully). However, these tools are easily available for hire at your local HomeDepot/Lowes (assuming you're in the US).

STAPLES

Now, I've never heard of anyone using staples for hardwood floors. It's more a carpet layer's tool. With staples, you'll also have to nail in through the face, thereby leaving marks all over the floor and ruining the appearance. You can probably use staples to lay down the backer board under the hardwood floor (if you're in a cold weather/windy area, this will help insulate the house by preventing airflow through the slots in the floorboard). Using them on hardwood floors is a terrible idea, and wouldn't recommend it under any circumstances.

Wall to wall carpeting is usually attached to the floor using carpet tack strips around the perimeter like these

The raised tack points grip the edges of the carpet.

Once you pull up the carpet, there is probably a padding that is just laid on the floor without adhesive. If it is rubber backed, the rubber bottom surface sometimes sticks to the floor underneath. Rubber residue can usually be scraped of with a plastic putty knife without damaging the surface of the wood underneath.

The tack strip can be pried up and there will be a few nail holes per strip that can be easily filled.

The real issue will be the condition of the finish on the floor once you get to it. If there is glue on the surface, this may be difficult to remove without serious sanding. Often the finish is fine and a cleaning is all that is needed.

If the finish is slightly worn or lightly scratched, a light sanding followed by a coat or two of polyurethane should restore it. Professional finishers have a light abrading process using large buffing machines that can do this easily and quickly. However it can be done with an orbital sander and lots of time and elbow grease. Very thorough vacuuming and wiping of all dust is essential for a good finish.

If the finish is badly worn or deeply scratched, a serious sanding and refinishing is called for. Again, it can be done by the DIYer, but this is a big job, sanding with power hand tools is very tedious and the professional sanding machines are difficult to use for the novice.