PC World is heading off customer fears about buying a Windows PC this Christmas by offering a free Microsoft Vista upgrade.

From today until March 2007, any PC or laptop priced at £399 or above in PC World will receive a free upgrade to Windows Vista Home Premium edition when it is launched next year.

Microsoft has already announced a coupon program that will allow computer buyers to upgrade for free or for a small fee to Windows Vista and Microsoft Office 2007.

Both companies are trying to head off slow sales this Christmas as customers wait for the next operating system to be released.

The new operating system offers a breakthrough user experience, designed to help you feel confident in your ability to view, find, and organise information and to control your computing experience.

Bryan Magrath, PC World's commercial director, said Vista was the most radical re-engineering of Microsoft's operating system in several years and the launch has been widely anticipated.

"We're delighted to be able to provide a Vista upgrade guarantee to all our customers in the important pre-Christmas period," he said.

"Our entire range of laptops and PCs priced at £399 and above have the muscle and the processing power to run Windows Vista effortlessly."

Anyone purchasing a PC below the £399 threshold will still be able to upgrade to Vista, with PC World charging half the recommended retail price, plus any post and packaging costs.