Regret your choice for Windows Vista? If you bought a license or product ID key to use Windows Vista, or Windows Vista was preinstalled as OEM version with your new laptop or desktop system, but now you decided to give up Windows Vista and back to Windows XP instead, the downgrade process from Windows Vista to Windows XP may not as easy as you think. Beside, unless you specifically buy a new license for your Windows XP, you may actually break the copyrights law of the state by using illegal non-genuine Microsoft software.

Microsoft provides a downgrade rights chart (downgrade_chart.doc) (no longer available) which stipulates the downgrade rights on whether you’re allowed to use prior version of software for Microsoft software acquired through Microsoft Select License, Open License (OPL), Original Equipment Manufacturer (OEM) License, and Full Packaged Product (FPP) License.

Again, Microsoft always treats big corporations and large companies better than retail customers (for obvious reason, corporate pays more). Select License and Open License priced software, which normally only corporate will acquire, are granted with all freedom and rights for all applications, systems and server software, including the possibility of dumping Windows Vista to use Windows XP. However, if you’re general public who acquired your Microsoft software through OEMs (OEM License) or purchased the software product from a retail shelf (FPP License), you probably out of luck.

Thus, for those seeking to legally down grade to Windows XP may have to buy a new Windows XP product key. Your previous OEM Windows XP serial key are not transferable. If you’re planning to use a Windows XP package retail license product key, you can only use it on one machine, so you will require to stop using that product key on the original machine. So you’re going nowhere.

Beside, the FAQ on downgrade rights also stipulates the version of Windows XP which the Windows Vista Business, Enterprise and Ultimate can downgrade to:

Can I downgrade my OEM version of Windows Vista Business to Windows XP Professional?

Yes. OEM downgrade rights for desktop PC operating systems apply to Windows Vista Business and Windows Vista Ultimate as stated in the License Terms. Please note, OEM downgrade versions of Windows Vista Business and Windows Vista Ultimate are limited to Windows XP Professional (including Windows XP Tablet PC Edition and Windows XP x64 Edition). End users can use the following media for their downgrade: Volume Licensing media (provided the end user has a Volume Licensing agreement), retail (FPP), or system builder hologram CD (provided the software is acquired in accordance with the Microsoft OEM System Builder License). Use of the downgraded operating system is governed by the Windows Vista Business License Terms, and the end user cannot use both the downgrade operating system and Windows Vista Business. There are no downgrade rights granted for Windows Vista Home Basic or Windows Vista Home Premium.

If I have Windows Vista Enterprise, what can I downgrade to?

Downgrade rights in the Volume Licensing programs provide customers with the right to downgrade to any prior version of the same product. Windows Vista Enterprise is a new type of product and does not have a prior version. However, customers licensed for use of Windows Vista Enterprise are licensed for Windows Vista Business, and it can be downgraded to the Windows XP Professional, Windows 2000 Professional, Windows NT® 4.0, Windows NT 3.51, Windows 98, or Windows 95 operating system. You would not, however, be able to downgrade to Windows Vista Home Basic or Windows Vista Home Premium, Microsoft Windows XP Home Edition, or Microsoft Windows Millennium as those are different products and not considered previous versions of Windows Vista Business.