Three of the top four PC sellers worldwide plan to sell systems with Windows XP right up to the Microsoft-mandated deadline of June 30.

Of the four, only Dell plans to call it quits before the last day of this month.

Microsoft has set June 30 as the final day of Windows XP availability to retailers and major computer makers, although the company recently also said that the date won't mark a sudden disappearance of the old operating system.

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"The exact cut-off day for selling Windows XP is determined by OEMs and retailers, who can keep selling standalone versions as well as PCs with Windows XP preloaded by OEMs distributed prior to June 30, 2008, as long as their supplies last [emphasis in original]," a Microsoft spokeswoman said two weeks ago in an e-mail.

Hewlett-Packard, Acer, and Lenovo -- ranked nos. one, three and four, respectively, in global PC sales in the first quarter by both Gartner and IDC -- will continue to sell XP-powered machines until June 30, the companies said this week in response to questions from Computerworld . Dell, which is the world's number two OEM, is sticking to June 18 as the last day that customers can order computers with XP pre-installed.

Here's what the OEMs said about their plans:

Hewlett-Packard: "We do still offer XP on a select number of our existing consumer notebook, gaming and business products," said a spokesman for HP. "This will continue through the XP end of life date on June 30, 2008."

Dell: Weeks ago, Dell said that it would stop taking customers' orders for PCs with XP after June 18. Wednesday, an e-mail from Dell's small business group titled "Last Chance" repeated that date. "It's time to decide if you want a Dell system with pre-installed Windows XP or Windows Vista," Dell's marketing e-mail read.

Acer: "For Acer, it's June 30," said a spokeswoman for the Asian OEM's American operations.

Lenovo: Although Lenovo spokesman Doug Bell first said his company's last-sale date was June 15, after checking, he confirmed that it is, in fact, the end-of-life June 30.

Some of these computer makers, however, will continue to sell PCs with factory-installed XP licenses after June 30 by taking advantage of Windows Vista's downgrade rights.

A clause in Microsoft's guidelines for OEMs lets computer makers install Windows XP Professional -- but not the more common and less expensive Windows XP Home -- on new PCs at a customer's request when those machines are ordered with Windows Vista Business or Windows Vista Ultimate.

Dell was the first to say it would use the downgrade clause to offer buyers XP Professional pre-installed long after the June 30 deadline. Those PCs will also include Vista installation media so that customers can, if and when they want, upgrade from XP. Dell, however, has not said how long it would offer the downgrade option.

Not so with HP. "HP has been offering business desktops, notebooks and workstations with the option to downgrade to Windows XP Pro from Vista since August 2007, and will continue to offer this option on its business systems through at least July 30, 2009," said the HP spokesman.

Lenovo, meanwhile, said it would continue to offer its downgrade option -- Lenovo doesn't swap out the Vista for XP at the factory floor, but instead sends media that requires the user to re-install Windows XP -- until Jan. 31, 2009.

Acer did not comment on how it will address downgrades.

June 30 is not Microsoft's final-final deadline for all computer makers. It will sell licenses to registered "system builders" -- smaller shops and individuals who acquire Windows through one of Microsoft's authorized distributors -- through Jan. 31, 2009. And the company has also recently extended the availability of XP Home to a subset of computer manufacturers who are, or plan to, build small, cheap notebooks and desktops, such as the Asus Eee PC.