(AB doesn't want to accept this ost, so I'll try splitting it into 2 parts):
There is no way that you can restore or overlay Windows to recover deleted files.
When you delete a file (whether by using 'Delete' or by saving another file with the same name), the file is not actually erased from your hard drive. All that happens is that the space it occupies is marked up as available for re-use. If your PC has not already written another file to the same space on your hard drive it might still be possible to retrieve it. (Over-writing a file, by saving a later version, doesn't actually use the same space so, even if you've done this, it may still be possible to retrieve the file).
It's important to remember that your PC is constantly creating all sorts of temporary files as you use it. Any one of these could be written to the space which previously held your precious file, so it's extremely important that you don't do anything with your PC which is not absolutely necessary. (Assuming that you're reading this on the affected machine, do not turn it off or do anything at all with it (i.e. no games, no word-processing and no further web-browsing) -other than what follows - until after you've made an attempt to retrieve the file.