Okay I know upfront that this is officially a no go. Right now I have one Windows 8 Pro upgrade disk that I bought before the prices went up about a year ago. Boot Camp supposedly does not allow upgrade installations of Windows. One way around this, is to install Windows 7 and then upgrade. I have a Windows 7 install disk for my desktop, but the but the key is already being used. I don't know if I run the Windows 8 Pro upgrade on a Windows 7 installation that is not activated. And I also have a Windows 7 install disk for a Samsung Series 7 Slate tablet. The Slate is currently not using Windows 7, but Windows 8.1. And the install disk was designed for a specific piece of hardware, certainly not Boot Camp. Another possibility is to install an older version of Mac OS X, such as Snow Leopard, on a bootable hard drive. That could allow me to install Windows XP on Boot Camp, and then upgrade to 8. But I'm not sure if it would allow me to install boot camp on a drive that is currently not the boot drive. My main hard drive is an SSD currently running Mavericks. And I don't know if Snow Leopard will install on a mid 2012 MBP, even if an external drive. My other option is to convert a Windows 8.1 VM on Parallels Desktop 9 to Boot Camp. I found a few articles here and there that describe how to do it, but none of them are for the faint of heart. Of course the simple direct route would be to purchase the Windows 8.1 full version. But that is quite expensive than I already have the existing upgrade disk, just not the proper OS upgrade from.