Just to confirm the posts above.
If you are confident it's PD, then you can do whatever you wish with it. Any derivative work of a PD work (such as a translation) is under a separate copyright belonging to the author of the derivative work.
Some rules of thumb (there are complications for unpublished, anonymously published, written for hire, works by governments, etc.):
If the work (text, image, etc.) was published in U.S. before 1923 (excluding 1923), it's public domain in the U.S. Even if it was published in U.S. in 1923-1964 (don't get tripped by U.S. reprints of works first published elsewhere), then it may still be in public domain (most books published at that time are); however, it is much harder to establish their PD status (it requires searching government records for copyright extension trying to prove the negative -- that the copyright registration was not renewed when it was supposed to).
If the work was published outside of U.S. and you are confident that the author, if known, must have died more than 70 years ago (or 50 years in some countries), then you can be confident it's PD.
If you would like to know more about PD, then I recommend the following book,
http://www.amazon.com/dp/1413312055/