Microsoft Corp. is giving Windows XP yet another reprieve, this time allowing custom PC builders to continue to order the older operating system for their computers until the end of May.

It's the latest move Microsoft has made to extend the life of XP in response to resistance from both consumers and computer makers to the software giant's Windows Vista operating system.

Windows XP was due to disappear on Jan. 30, 2008, to make way for Vista, which had a high-profile launch in early 2007.

But Vista's unpopularity with consumers has forced Microsoft to extend the life of the older operating system.

Larger PC makers, including Hewlett-Packard and Dell, had their deadline to offer XP extended until June 30, 2008, though even after then consumers can "downgrade" to XP at an additional cost.

The latest extension affects smaller, custom PC makers who originally had until Jan. 31, 2009, to place orders for XP licences, but now have until May 30 next.

Microsoft has already said it will end support for the consumer version of XP in April 2009, while the company will continue to support the business version of the software until 2014.

Manufacturers of smaller, lower-power laptop computers, or "netbooks," can also continue to offer XP until June 30, 2010, as these computers do not offer Vista.

Microsoft has already announced it is developing Vista's successor, Windows 7, which is expected to be released as early as the end of 2009.

Windows remains the dominant operating system for computers, but in November its share of the market dipped below 90 per cent for the first time, according to an internet measurement company.

In November, 89.5 per cent of internet users who connected to websites monitored by Net Applications Inc. used Windows as their operating system, a decrease of 0.84 per cent from October.

The decline was the biggest in the past two years, the company said, and offset a number of recent gains.

The study combined the totals from three versions of the operating system in its study: Vista, XP and Windows 2000.