I don't know what "choose loop0" means either but I'm sure it doesn't belong in end user install instructions from Windows.
I attempted to install the 64 bit Linux Mint 13 Ubuntu (Cinnamon) edition from inside 32-bit Windows 8 Developer Preview. It failed, possibly for the 64 vs. 32 bit reason but also possibly because of a complex disk configuration.
There is a serious flaw in the language used by the installer in any case: It says at some point in the installation to "reboot" to continue the install, but it's unclear whether one must reboot into Windows (whcih started the install) or the new Mint install, or what. if it doesn't matter, it should say it doesn't matter. But if there's any chance of getting this wrong due to a grub issue or just putting the installer on a different disk than the ordinary boot disk, the installer must be absolutely clear *WHAT* to reboot into. In my case I attempted reboots into both but I got what appeared to be an NTFS error (it was an NTFS disk Mint was installing to) that I had the Windows 8 recovery tools fix.
So unfortunately the installer fails. Either because it's not working or because it's so poorly documented that many common cases will require fixes ordinary users aren't capable of. Ubuntu is losing ground to Mint largely because of a bad installer, I suggest this be fixed ASAP. Also, make it very easy to report bugs, using a wiki without a login, or you'll just not hear of them.