Windows XP = Kernel version 5.1 AND kernel version 5.2
Windows Vista = Kernel version 6
Windows 7 = Kernel version 6.1 (WTF OMG so retarded)
Windows 8 = Kernel version 6.2
I know they want to be all pure about their major numbers and whatever, but really they should just get over it. Windows7 is a major release different to Windows Vista, regardless of whether the NT people think it's a pretty minor change.