Publishing : Copyright and Public Domain

I`ve been trolling around trying to find an answer to this one on a number of boards, and have yet to find it.  Since I can relate it directly back to my desire to be in business, I`ll post it here as well .The question is about the line between public domain and copyright.  I`ve come across some public domain works that I think would be of great value to my market.  I`m sure they`re public domain, they`re over 100 years old, etc etc etc..  What I`d like to do is take the original source, modernize it a bit, and republish in some more modern ways (ebook, podcast, etc...)So, here`s my question.  I can find a dozen different "free" directories on the net that make this public domain stuff available.  But then they go and put their own copyright on the actual text.  I don`t think there`s anything inherently wrong with that - they`re copyrighting their version of the original, which would mean the format they chose, the typos they forgot to fix when transcribing, and so on.  But what I`m wondering is, how do I get my hands on a truly public domain document to use as the source for my own publishing efforts? I can`t simply take someone else`s copyrighted document and start hacking on it.  I figure I have a couple of options -- either take a copyrighted edition and then just modify it as to be unrecognizable from the original (don`t love that one), keep searching until I find someone who has put up a PD licensed version (not impossible - I have Shakespeare that way), or else find a paper copy and transcribe it myself (don`t love that, and besides I think the paper publication would also have a more modern copyright).  Any suggestions?Second question is, once I get my hands on the PD source, what am I really allowed to do with it?  I figure the options range quite a bit:- just republish it, as is, the same document from 100 years ago just brought into an electronic form.  This is quite common in the ebook directories, as I`ve mentioned. - "wrap" it by adding my own introductory matter and other content, but basically leave the original alone.  Call myself the author and attribute original source appropriately.- hack and slash at will.  Cut out and change what I don`t like, and insert freely.  Call myself the author, but cite the original source someplace in tiny print nobody will see   The trick here would be how you present the work and whether it`s clear to the reader that you are amending an original or if he thinks you wrote the whole thing.The first question is really the crucial one since it goes directly to legal issues, plagiarism and so on. I don`t relish the thought of Oprah tearing me a new one when I get big and famous.   As for the second question I`m trying to figure out the ethical line between the latter two options.  I definitely want to add value to the original, not just republish it, but I`m unclear when it becomes my own work (which would give me some established cred as an authority in the field) versus just a republication of the original, which anybody can do.  Thanks!