odds are actually better then you think. I had to use one of these on my roommates computer so I scanned mine just for kicks. I found some OLD files that had survive two or three reformats and installs. Part of it was they were on a partition at the very end of the drive that was deleted and replaced with a larger partition further up on the drive, so no data was written to those sectors.
If it's a fresh install and you haven't done much else, I'd say chances are better then dismal since windows does tend to use the same part of the disk for it's stuff, so most of the overwriting would be done to windows files and not necessarily your saved documents. Just try it and see