Hi Mick248. Unfortunately the file extension .dat is used for almost any data file type. The only way to interpret these files is by knowing what generated them. As you've tried opening the files as jpegs, then unless you know of another format the pictures may have been in - possibly a proprietary format that the camera uses, then tha chances of recovering the pictures are slim.
You say that your friend copied the photos from the camera to a CD-RW. Unless the pictures were first copied to a folder on the computer, this could have been the source of the problem. Also I would never trust "drag and drop" packet writing onto a cd-rw disk for photos as this is notoriously flakey.