The study.

This is the floor we sacrificed so that we could fix the others.  We decided to use this one because it was the worst -- it had the most holes.  And some of them were really big.  Here's what it looked like after most of the top floor was pulled up:

study1.jpg (29848 bytes)One thing that's pretty neat about this is that you can see the subfloor (the boards running across the picture rather than up and down).  These are the original oak floorboards in the house, and some of them are almost 20 inches wide.  Unfortunately they're quite badly damaged, and very difficult to replace.

study3.jpg (27643 bytes)This is the pile of floorboards we pulled up from this floor.  We used most of these to patch the other rooms.  We pulled them up using a crowbar and a lot of elbow grease.  Some of them were wider than we needed downstairs, so we used a table saw to strip them down to the right width.
study4.jpg (18686 bytes)After we got all the debris out of the room, we laid down pieces of plywood across the entire floor and covered that with a ready-made hardwood floor surface.  We used a shiny oak. This is how it looks now.  (Except now our furniture is here, so the room is full of books and computer stuff.)