IIRC then new file may not of been written to the same part of the disc so you should be able to recover it. Also even if it did write to the same starting sector there size should be smaller and it just the link to the data on the data is self that is gone.
First things first, make sure NO MORE writing to the drive is done, so power down the PC. The get out a copy of your fav. data recovery software take it for a spin...
If the old data was not writen over at least 3 times since the deletion but should/maybe able to get it back. But think first is the data really worth your time or is it more cost effective to get the user to just recreate the original document.
*/ Edit: This Post from The Denv may come in handy */