Dell is actively promoting a Microsoft licensing loophole to channel partners eager to keep selling PCs installed with Windows XP, after Microsoft's official cut off.

The Dell channel blog is pointing resellers to the loophole in the Windows Vista license that enables business customers to downgrade from the unwanted Windows Vista to its dated, but comfortable and better-supported predecessor.

According to the blog: "Dell can sell what we've branded 'Windows Vista Bonus' which allows us to preinstall XP Professional with a Vista license (on select system categories). This lets customer's upgrade to the Vista platform when they're ready. And yes, Dell will support both OSs."

Dell's blog points resellers to further information here.

Dell, meanwhile, is also making Windows XP available as an image to those partners using the company's Custom Factory Integration service.

The blog was designed to coincide with the last day Windows XP was officially available from Microsoft. From now on, you can only get Windows Vista. Officially.

Dell has taken a leading position in continuing to offer Windows XP. Earlier this month Dell vowed to keep selling PCs running the operating system until "at least 2009".

Dell's stance of not just offering Windows XP directly but actively telling its huge ecosystem of resellers how they, too, can game Microsoft's system and continue selling Windows XP demonstrates a significant shift in the OEM's relationship with Microsoft.

With chief software architect Bill Gates' departure fresh in the air, it should be remembered how, under Gates' tenure last decade as chief executive, Microsoft exploited its position as supplier of a popular PC operating system to play hardball with PC OEMs on licensing Windows.

During the US Department of Justice's antitrust trial, IBM revealed that Microsoft had delayed giving IBM access to Windows 95 simply because IBM refused to kill its own OS/2 operating system or agree to not bundle its SmartSuite rival to Office on IBM PCs.®