The introduction of Service Pack 1 for Windows Vista and of Service Pack 3 for Windows XP, along with the June 30 retail and OEM availability cut-off date for XP, have generated a consistent a mount of confusion over the future of the two Windows clients. Especially over Vista's predecessor in terms of its retirement from the retail and OEM channels, but also in regard to support and downgrade rights. As far as support is concerned, XP SP3 will live to see 2014 (read more about it here). And when it comes down to Vista SP1 to XP SP3 downgrades, nothing has changed from Vista RTM and XP SP2.

"You will still be able to get Windows XP Professional installed on computers after June 30th. This is more important for sysadmins who have a large current installation of Windows XP-based systems and have not yet migrated to Windows Vista. If you're a consumer, consider getting a new computer with Windows Vista installed: with Business and Ultimate, you have downgrade rights to XP Pro," revealed the Chief of Staff of the Windows Core Operating System Division at Microsoft.

Downgrade rights permit end users to access two versions of the Windows operating system, in this context either Vista or XP, with the same license. Namely, a single OEM license permits customers to install XP, and subsequently remove it and deploy Vista on the same machine. Microsoft is essentially interested in offering clients the ability to buy Windows Vista, but continue to run Windows XP until they are capable of moving to the latest Windows operating system.

Essentially, OEM versions of Vista Business and Ultimate versions with a downgrade license allow users to install and run XP Professional, XP Professional x64 Edition, and XP Tablet PC Edition. This is also valid for the Service Pack 1 variants of Vista, respectively for XP SP3.

"End users who downgrade may reinstall the original software when they are ready to migrate. For example, an end user who downgrades to Windows XP Professional may later return to Windows Vista Business software provided that the end user deletes the Windows XP Professional software from the PC," the COSD lead added.