Piriform do a great free file recovery tool called recuva, which I highly recommend. Take a look at
www.recuva.com.
I've used it several times to recover files when friends or relatives have accidentally deleted important files on their PC's. I carry a copy everywhere on one of my USB sticks (along with portable versions of Piriforms other free apps CCleaner and Defraggler plus others like the full Sysinternals suite of system diagnostic tools, Cain and abel etc. etc...)!
As the other posters have already stated, once you've deleted a file, the space it used to occupy is basically open to being overwritten and could be overwritten by the system at any time.
But usually, as long as you're quick with your recovery tool (and as long as you're lucky), you should be able to recover most, if not all of your files!
After installing Recuva on your PC, you can create a portable version of the app to go onto a USB stick. To do this, open up your program files directory (or wherever you installed Recuva) and copy the entire Recuva folder to a USB stick. Open the Recuva folder on the USB stick, right click and select 'new->text document' to create a new text file and rename it portable.dat. This will cause Recuva to create and use an ini file in the folder on the USB stick to store user preferences instead of making regsitry entries.
Now you have a copy of Recuva which you can take anywhere with you. Next time you or someone you know accidentally deletes something on any windows PC, all you need to do is plug in your USB stick, fire up Recuva and recover the files!
This post has probably arrived too late to recover the files you've posted about, but having a copy of Recuva could save your backside further down the line!