When Microsoft releases a new Operating System, they allow users of their previous Operating System to continue using the older version if they wish. The license for the new Operating System can be used as a license for the old; this is known as downgrade rights. Microsoft's Windows Vista can be downgraded to Windows XP, and Windows 7 can be downgraded to Windows Vista or XP. In both cases be sure to have a valid copy of the downgrade OS with matching Product Key for use during installation and activation.
Only owners of OEM editions of Vista Business or Vista Ultimate can qualify for a downgrade to Windows XP Professional, including Tablet PC Edition and x64 Edition. Two versions of Windows 7 have downgrade rights: Windows 7 Professional and Windows 7 Ultimate. Windows 7 Professional users can downgrade to Windows Vista Business or Windows XP Professional; Windows 7 Ultimate users can downgrade to Windows Vista Ultimate or Windows XP Professional. These downgrade rights will be granted for the entirety of Windows 7's life cycle.
INSTRUCTIONS FOR COMPLETING THE DOWNGRADE PROCESS
To complete the downgrade, install Windows XP or Windows Vista as normal (see Knowledge Base articles below for more details). When prompted to enter a Product Key, use any applicable Product Key that is available. For example, if installing Windows XP Professional, use any Windows XP Professional Product Key. When prompted to activate, choose the Activate by phone option. This option will generate an Installation ID that will be used for the activation process. However, rather than entering the Installation ID as directed, enter it incorrectly so that the call is transferred to a Microsoft Representative. Explain to the Microsoft Rep that this install is utilizing downgrade rights, and the rep will request the following information be emailed to them -
The recently purchased Windows 7 and/or Windows Vista Product Key(s) (PID)
Once the above information is confirmed to be valid, they will email back a Confirmation ID for each system; this typically takes anywhere from 30 Minutes to 5 business days. The Confirmation ID is used to complete the remainder of the activation process.
For more information on Windows Downgrade Rights, please visit the following pages -