You can't? Why not? I have a Boot Camp + Parallels installation of Windows XP from a 'Get Genuine Kit for Windows XP Professional' which it says somewhere it's OEM. Since it's target at legalising XP installations, I legalized it, I even have a XP OEM sticker on that Mac (yeah, looks ugly on a mac, that's why it's in the battery compartment ;P). The only downside is, I cannot transfer this installation to another computer.
EDIT: It's actually an OEI DSP license and not OEM.
Last edited: Jun 17, 2008