You could have a look here click here for locating duplicate files - I don't know what it's like as I haven't used it myself (I just collect links posted here to what I think might be useful at sometime in the future!).
With rgard to backing up you could have a look here
click here, which should give you plent of reading.
If these are not any use at least it's bumped you up the list until somebody more knowledgeable comes along!