Removing old oak flooring can be very difficult. When it was installed originally, the installers usually put it down so it would never come up. We have removed a lot of hardwood floors over the years, however, it was never removed to be saved. It’s way too labor intensive. The wood wants to split when removed. With that being said, you can remove it, but it will be a labor of love, if you know what I mean. Each board will have to be pried up a little to raise the nail head, then the board moved back down and hopefully the head stays raised so you can get a nail-pulling tool on it. Most hardware stores sell assortment of nail-pulling tools. Two that I have used are the cat’s paw and end-cutting pliers. You may decide to save just enough wood to make a cool table or finish off the flooring in a small room. If you can get it all saved, I think you’ll find that there is a market for salvaged wood like this. EBay would be a good place to put an ad. Let me know how it goes for you.