Microsoft is to extend the availability of Windows XP by two years.
But the extension will apply only to extremely specialised low-end PCs, and not to common consumer models.
A company spokesperson said that availability will be limited to PCs classified by Microsoft as "ultra-low cost" .
"We believe that Windows Vista is the best way to address customer and partner needs on mainstream PCs," said the spokesperson.
"But Microsoft recognises a growing class of hardware-constrained, lower-cost PCs that would benefit from a different Windows-based solution.
"While Vista provides an easier and more secure user experience, XP Home provides an effective solution on these devices from a performance and cost perspective."
Microsoft had originally planned to stop shipping new copies of XP to hardware vendors on 31 January 2008.
However, after PC makers lobbied the company to extend the deadline, Microsoft moved XP's termination back to 30 June.
The company said that this deadline will remain in place for most machines, forcing vendors to offer Vista on most new PCs.
"We are very proud of the progress we have made with Windows Vista over the past 16 months," said Michael Dix, general manager of Windows client product management.
"Given this landscape, and after consulting with our partners, apart from today's announced extension of Windows XP Home for ultra-low cost PCs, we are maintaining the timelines we announced in September."