Hmmm.
From the Magical Jellybean website:
If you purchased your PC with Windows already installed from a large manufacturer such as Dell or HP, it's likely that Windows was installed using an OEM key instead of the actual key for your PC. This saves them (and you) money because it's much more efficient for these large companies to install Windows once and then clone the drive.
Does this mean the OEM key is right there on the CD? If so, I probably got one of those. Or do they use a regular CD and enter the OEM key?
And cloning a drive to install in another PC (with the same mobo) will usually work, too.