Try Recuva from
http://www.piriform.com/recuva/download - it is free by the way.
If you have a memory card reader on your computer, put the memory card in it and then use the software to recover the deleted files. If you don't have a card reader, attach the camera to the computer and see if it will work that way - with luck the computer will see the memory card as a removable drive and the program will let you recover the files.
I haven't used this program, but it is a recommendation from a site I trust, and it's from the same people who wrote Ccleaner which I do use regularly.