The windows 8 install.wim file is simply placed onto a windows 7 install dvd in order to get it installed. Then after that it boots from the HD on its own.
I think if you read the EULA however it says Windows 8, which should only be a minor trick anyways.
A good way to check what version you are really in is to open a command prompt, it'll tell you the version number right there. Install DVD will be 7600 and then once you boot off the HD you'll be at 6.2.7959.
7959 is a 64-bit Server version leak and R2 was just the previous server version.