Microsoft has admitted that Windows XP's new lease of life is to be continued well into next year.

A leaked memo from HP has revealed that the venerable operating system will not only be offered as a downgrade from Vista but also from the forthcoming Windows 7.  Microsoft has acknowledged that it has "broadened the options" for PC makers regarding Vista, although the company would not confirm specific reports that HP had been given the green light to sell new PCs with Windows XP Professional preinstalled until the end of April 2010.

"Based on feedback, Microsoft is further broadening the options provided to Direct OEMs to help customers facilitate End User downgrade rights included in the product licence terms of a new system with either Windows Vista Business or Windows Vista Ultimate," said a Microsoft spokeswoman. "This option is designed to help Direct OEMs further support customers, primarily small business customers, looking for Windows XP Professional due to application compatibility concerns."

The Microsoft comments follow reports on AppleInsider, citing a leaked HP memo, that the company had given HP the okay to offer Windows XP as a downgrade until the end of April next year.

"Downgrade" describes the Windows licensing rights that allows users - and in their stead, computer makers - to install Windows XP Professional while also providing media for Vista for a possible upgrade later. In effect, the licence for the newer Windows - Vista - is transferred to the older edition, XP. Microsoft allows owners of only Vista Business and Vista Ultimate - the two highest-priced editions - to downgrade to XP.

Windows XP went into semi-retirement in June 2008 when Microsoft stopped selling it at retail and withdrew Windows XP Home from use on all but netbooks, though it allowed XP Professional to be installed as a Vista downgrade. Since then, Microsoft has extended the final date it would sell XP Professional install media to large-sized computer makers and smaller system builders to 31 July 2009 and 30 May 2009, respectively.

Today, Microsoft denied that it had extended the lifespan of Windows XP, and intimated that those rights were built into the newer OS - in this case Vista - and did not expire at some arbitrary date. "End User downgrade rights are a right in the end user licensce for Windows Vista Business and Ultimate products, and therefore remain in effect for the life of the product, so this change does not represent an extension."

However, the company did not answer questions about whether it was extending the availability of XP media, a crucial factor for OEMs, who must have those installation or restore discs to include with the downgraded PC. When Microsoft said in October 2008 that it had extended media availability another six months, until July 2009, a spokeswoman had stressed the importance of media availability in downgrade scenarios. "The [downgrade] rights don't go away. It's all about having the media on hand," she said then.

The internal HP memo cited by AppleInsider also claimed that Microsoft would also let computer makers downgrade new PCs from the next operating system, Windows 7.

"Microsoft will allow PC OEMs to structure similar downgrade OS SKUs for Win 7 Professional once available," the memorandum read, said AppleInsider. You can anticipate that business desktops, notebooks and workstations will take advantage of this with the release of Win 7 in the October timeframe to allow our customers maximum headroom as they transition away from XP Pro OS."

The Microsoft spokeswoman denied that any termination date had been set for Windows 7 downgrades, but implicitly acknowledged that they would be available for at least a time. "No dates have been announced for the end of Windows 7 downgrade right facilitation to Windows XP," she said.

If the HP memo is accurate, Windows XP will be available for more than a year after Microsoft shifts the aged operating system out of what it calls mainstream support, and into the more limited extended support phase. Windows XP will drop out of mainstream support on 14 April.

HP did not immediately reply to a request for comment on the XP extension.