Microsoft Corp. has once again extended an impending deadline for Windows XP's demise, the company confirmed today.

System builders—the smaller shops and computer dealers that build PCs to order—will now be able to obtain Windows XP Professional licenses through at least May 30 and likely long after, according to a Microsoft spokeswoman. Previously, Microsoft had set Jan. 31 as its deadline for selling new XP licensees to the distributors that supply system builders.

"Microsoft is making accommodations through a flexible inventory program that will allow distributors to place their final orders by January 31, 2009, and take delivery against those orders through May 30, 2009," said a company spokeswoman in an e-mail.

The relaxed rules directly affect Microsoft's authorized distributors, which in turn sell licensees to system builders. Previously, the middlemen distributors, which include well-known names such as Ingram Micro, were told that they had to not only place orders for XP licenses by Jan. 31, but also take possession of those licenses and, of course, pay for them.

Rather than require distributors to stockpile licenses prior to the Jan. 31 deadline, Microsoft will now only demand that they place their orders by that date. Under the new plan, they will have until the end of May to actually take delivery of, and pay for, the licenses.

System builders will be allowed to purchase licenses from distributors until the latter exhaust their supplies, which means that custom computer makers will have access to Windows XP Professional until at least May 31, and assuming distributors have licenses remaining in stock, for weeks or even months after that.

The pay-as-you-go plan is the most recent move by Microsoft in a series that has repeatedly lifted restrictions once put on the seven-year-old Windows XP.

In early October, for example, Microsoft added six months to the availability of Windows XP for larger computer makers, dubbed OEMs, for "original equipment manufacturers." Rather than cut off OEMs, such as Dell Inc. and Hewlett-Packard Co., as of Jan. 31, Microsoft shifted the deadline for obtaining Windows XP Professional media to July 31, 2009.

OEMs include Windows XP discs with new PCs that they had "downgraded" from Windows Vista at customer request. The end-around XP's retail sales retirement date—June 30, 2008—is a popular means for users to purchase new systems with the older operating system preinstalled. By some estimates, more than a third of all new PCs are downgraded from Vista to XP.

Dell, for instance, has been selling downgraded PCs at a markup of $150 above the cost of equipping the machine with Vista Home Premium, the most popular, but not the priciest, version of the newer operating system.