You can try odorless mineral spirtis, and if that fails lacquer thinner. And lastly Goof-Off (www.goof-off.com). Squirt the solvent under the paper and try pushing it off with a good quality putty knife.
If all that proves ineffective try a safe paint stripper (Citristrip at www.cirtistrip.com). Also read my article on this great stuff in the Floored News section. But as a last resort you can use some of the more dangerous methyline chloride strippers, just leave the house as the stripper does it's work.
And you really must be diligent about removing all this tar paper. It may be glued with an asphalt cut back adhesive, and these can never be sanded off, because of the asbestos concern. It may be best to have it tested for asbestos before you get much further.
As always your Most humble servant, Joseph, the Wood Floor Doctor.
You may also find these articles helpful:
1. How To Clean And Maintain Wood Floors PART ONE
2. How To Clean And Maintain Wood Floors PART TWO
3. How to remove and clean various stains and odors from wood floors
4. Floor Types And Finishes
5. How To Take Care Of Your Health And Safety when Installing, Finishing, Repairing or Cleaning your wood floors