Best way to clean hard wood floors? See pic.?

I have wood floors that I just discovered under old carpeting. I uploaded the photo to my yahoo profile. There is all kinds of. . .I dunno, carpet glue? still stuck to the floor. It is really old and is pretty content with staying there. I dont want to damage the floor but really wanting to get them clean. If someone could please take a look and let me know what is the best way to clean them I'd really appreciate it! Thanks!! :)