Sorry , so what you've actually got is the IMG file. I sort of read it that this was rarred up.
You have several ways of dealing with this.
Typically you would burn this straight to a Cd or DVD depending on the image type.
However, it can be mounted on a virtual drive like Daemon Tools & then accessed through explorer.
Or you could open it up with the likes of MagicISO, ULtraISO or ISOBuster.
Have I now understood the problem correctly?