Despite its big push for Vista, Microsoft is quietly allowing PC makers to offer an option that lets users "downgrade" to Windows XP, allowing customers to purchase new PCs but stick with the older operating system.

The program applies only to Windows Vista Business and Ultimate versions, and it is up to PC makers to decide how, if at all, they want to make XP available. Fujitsu has been among the most aggressive, starting last month to include an XP disc in the box with its laptops and tablets.

"That's going to help out small- and medium-size businesses," Fujitsu marketing manager Brandon Farris told ZDNet Australia sister site CNET News.com.

Hewlett-Packard also started a program in August for many of its business models. "For business desktops, workstations and select business notebooks and tablet PCs, customers can configure their systems to include the XP Pro restore disc for little or no charge," HP spokeswoman Tiffany Smith said in an e-mail. She said it was too soon to gauge how high customer interest has been. "Since we've only been offering [it] for about a month, we don't really have anything to share on demand."

A Microsoft representative confirmed there were changes made over the summer to make it easier for customers to downgrade to XP. Under Microsoft's licensing terms for Vista, buyers of Vista Business and Vista Ultimate Edition have always had the right to downgrade to XP, but in practise this could be challenging. In June, Microsoft changed its practises to allow computer makers that sell pre-activated Vista machines to order Windows XP discs that could be included inside the box with PCs, or shipped to customers without requiring additional activation. Microsoft noted in a statement that neither it nor the PC makers are "obligated to supply earlier versions to end users under the end user licensing terms."

While there is always resistance by some to move to a new operating system, there appears to be particularly strong demand, especially from businesses, to stick with XP.

One of the challenges, for both businesses and consumers are Vista's hefty graphics and memory needs.

Lenovo, for its part, has details for its downgrade program on its IBM ThinkPad Web site.

Dell spokeswoman Anne Camden said Dell has been offering businesses that have a Premier Page set up the option to order systems with XP, Vista or Vista with XP downgrade rights. There is no extra charge for the downgrade rights.

"We've been offering it and we're still offering it," she said.

HP, Gateway and others also still sell machines with XP on them, nearly a year after Microsoft first started offering Vista to businesses. Vista went on sale broadly to consumers in January, at which point XP largely disappeared from retail shelves.

However, demand for XP has remained. In April, Dell brought XP back as an option even on consumer PCs.

There is an issue, though, over how long PC makers can keep selling machines with Windows XP as the preloaded operating system. Microsoft is requiring large PC makers to stop selling XP-based systems as of January 31, though some PC makers would like to sell XP machines for longer.

"We're all lobbying for it," Farris said.