Microsoft has announced it is extending its option that allows purchasers of new PCs and laptops the chance to downgrade from Windows Vista to Windows XP by six months.

The move comes even as Microsoft has just launched a $300m (£150m) marketing and advertising campaign to encourage people to buy Windows Vista. The company is also prepping Windows 7, the next client version of the OS, for release in the next 12 to 18 months.

Microsoft will give OS discs to original equipment manufacturers (OEMs) and system builders so customers that purchase the Windows Vista Ultimate and Business editions can downgrade to XP Professional until July 31 2009, Microsoft said.

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Previously, Microsoft planned to provide the XP recovery disks to partners until January 31 2009, although there is no deadline for downgrade rights, the company said. If a customer wants to downgrade from Vista to XP after the new deadline, they can contact Microsoft for a disk, the company said.

Microsoft predicted that Vista, which was released on January 31, 2007 and took more than five years to develop, would be the most successful launch of its Windows client OS. However, Vista has been riddled with glitches and bad publicity, and many businesses and consumers still prefer XP.