Deleted files (including images in memory cards) can be recovered under certain circumstances. If you didn't write any new files into the memory card (i.e., if you didn't take new pictures after deleting those you want to recover), you have a pretty good chance of recovering everything... but the more you used the memory card after deleting your pictures, the less will be the odds of recovering all of them.
You can try the PC Inspector Smart Recovery: it's a *free* Windows program that can recover many different kinds of image files, including Jpegs. You'll also need a memory card reader, though, so if you don't already have one you should borrow or buy one.