This could be a very long and labor-intensive project, depending on how much "paint" there is. How much of the floor is painted? It sounds funny that somebody would paint over Pine floors that were finished at one time (unless maybe in a hallway or stairs??). I have stripped and sanded paint off floors, and it is not fun. A heavy-duty stripper will be good for starters. Then you will need rough sandpaper (20 grit) to loosen and residual paint left over. Then finer sand paper to smooth it out. This is just from my experience, I'm sure others will have more to say. More information would also be helpful.