Microsoft has quashed rumours that it was looking at extending the retail shelf life of Windows XP.

Bill Veghte, the senior vice president who leads the company's online and Windows business groups, reiterated that June 30 is the deadline for Microsoft to halt shipments of boxed copies to retailers and licensing the OS directly to major computer manufacturers.

However, Veghte did leave the door open to all computer makers, even the largest, who want to continue selling new PCs with XP preinstalled.

"Additionally, systems builders may continue to purchase Windows XP through authorised distributors until January 31, 2009," he said, repeating existing policy that lets small-sized computer builders obtain XP from other dealers.

"All OEMs, including major OEMs, have this option," said Veghte.

Most major PC makers, however, have effectively called a halt to general XP-equipped system sales. Many OEMs, including Dell and HP will continue to offer the older operating system as a 'downgrade' option from Windows Vista.

Veghte touted that approach himself. "This is great value because it lets you use Windows XP on new PCs today if you need it and then make the move to Windows Vista when you are ready, without having to pay for an upgrade," he added.

Elsewhere, Microsoft re-emphasised that although XP will be tougher to buy after next Monday, it will not disappear overnight. In a new FAQ on its website, it said that retailers and computer makers were allowed to sell out their stocks.

"You may still see copies of the software or computers pre-loaded with it for months, as stores and PC makers work through their inventory."

And Veghte reminded users that Microsoft will support Windows XP for several more years. According to previously-scheduled timetables, XP continues in "mainstream support" until April 14, 2009, and won't be dropped from "extended support" until after April 8, 2014.