Dell will continue to install Windows XP on new PCs after Microsoft's June 30 retirement date by taking advantage of a little-known clause in the downgrade rights that come with Vista Ultimate and Vista Business.

"Dell has the ability to exercise 'Windows Vista downgrade rights' on your behalf in the factory if ... you'd prefer to have Windows XP Professional preinstalled on your PCs," Dell said on its Web site.

According to Dell, it will factory install XP after June 18 when customers choose a "Vista Ultimate Bonus" or "Vista Business Bonus" option as they configure PCs. Dell will then install Windows XP on the machine, and include backup media for that OS as well as the installation disc for Windows Vista.

A Microsoft spokeswoman confirmed late Friday that Dell was within its rights to factory-install XP on machines sold with a Vista Ultimate or Vista Business license.