yeah mate I understand what its like with file types and computer jargon and crap and how daunting and how mind boggling it can be as i use to teach seniors and disabled groups 101 computers.
Dat files are not usually graphic files . a dat file can accompany a graphic file as it contains instructions of how to display the file and where and when it was created and how and whom by and what with.
If you can open a file and display it on your pc then the file is complete but Im guessing the file is only half there and could be an idea to track down your mates email address and have them re sent, Perhaps as jpegs .
If you can open them they are complete and I can convert so feel free to Pm me and shoot the thru to my email .