I would not create any new files on the hard drive, becuase the new files may over write the old ones. Since Windows (I'm assuming you use Windows) writes all sorts of junk to drives its connected to, I wouldn't connect it to a computer unless you are recovering the files.

To recover the files, I use PC Inspector File Recovery, which can be found at download.com. Its for Windows only though. To recover the files, just run the app, open the drive with deleted files and use the file browser to find the lost files. Once you find them, you can save them.

Last tip, when you find the deleted files, I would save it to another drive, as saving files to the same drive with the deleted files might corrupt the recovery process. Hope this helps.