Dell has extended the availability of systems preloaded with Windows XP, citing customer demand for the older operating system.

The vendor started to charge purchasers of certain lines to downgrade the operating system from Vista to XP last week.

However, Dell has said on its website that XP machines will still be available in the Inspiron and XPS ranges.

"We are able to offer the opportunity to purchase a Dell desktop with an OEM Windows XP licence until 26 June at 5.59am central time," said the company.

"After 26 June you have the option to purchase Windows Vista Business or Windows Vista Ultimate with a downgrade service to Windows XP Professional.

"This option will be available on XPS 630, 720 H2C and M1730 systems. After 26 June, Windows XP will no longer be offered on currently available Inspiron laptops and desktops."

Microsoft has said it will stop selling XP licences on 30 June, except for low-end systems like the OLPC. However, Dell, HP and Lenovo have all said that they will continue to sell XP as a downgrade option.

The decision reflects the continued unpopularity of Vista among customers and developers.

Microsoft has already extended the deadline for XP by six months but is unlikely to do so again.