After examining the license agreement for Windows 8, it seems that Microsoft has continued their usual practices in regard to downgrading OEM versions of their Pro operating systems. Those who have the professional version of Windows 8 pre-installed by a manufacturer, will have the right to revert to an earlier operating system without being charged for it. But they will only be able to change to Windows 7 or Vista. Windows XP will not be included in this downgrade process.
Downgrade rights will not be allowed for those who purchase a retail version of Windows 8, nor for those with the basic version.
If the customer wants to downgrade, they will be responsible for obtaining the installation media for that older operating system, but this is the same as in the past. The license reads: Neither the manufacturer or installer, nor Microsoft, is obligated to supply earlier versions to you. You must obtain the earlier version separately.
Downgrading is going to be slightly more complicated with Windows 8, since it makes use of some of the features offered in UEFI compatible motherboards. You will need to set the bios to Legacy mode to install Windows 7 according to the Greg Keizer at ComputerWorld.
OEM's will be able to downgrade computers to Windows 7 at the factory for a couple of years according to the license. It will be interesting to see if they do so. This was fairly common when Vista first came out, and people refused to change from XP.
You can read more on the story here.
