Windows XP is proving harder to kill than a Halloween vampire. With businesses having all but shunned Windows Vista, Microsoft has decided to extend the period in which it will make copies of its older sibling available to PC makers.

Microsoft originally planned to stop distributing Windows XP media to large OEMs on Jan. 31, 2009, but this week said it would move the deadline to July 31 of next year.

A Microsoft spokesman claimed in an e-mail that the move is designed to help businesses upgrade to Vista painlessly. "As more customers make the move to Windows Vista, we want to make sure that they are making that transition with confidence and that it is as smooth as possible. Providing downgrade media for a few more months is part of that commitment," the spokesman said.

The fact is, however, that very few large companies are eyeing Vista. A survey released last week by the UK's Corporate IT Forum showed that only 4% of businesses in that country are using Windows Vista on workplace systems, while 35% said they were "not yet interested" in Vista. 58% said they were still using Windows XP, now seven years old.

A document obtained by InformationWeek last week revealed that state IT officials in Maine will likely skip Vista and stick with XP until Windows 7 becomes available sometime in 2010. Users have complained about Vista's resource requirements, intrusive security measures and lack of compatibility with older software.

Vista's unpopularity in the business world may have forced Microsoft to extend XP's shelf life. The company officially retired the OS in June for most markets, but continues to make XP Professional available to PC makers who offer it as a "downgrade" option from Vista on business systems. Downgrade availability was set to end on Jan. 31 but will now continue through next July.

If Microsoft is on schedule with Windows 7, that will leave a gap of just six months between the end of the XP program and Windows 7's availability. It's a sign that Microsoft has conceded that Vista has flopped in the corporate market.

Microsoft is hoping Windows 7 will receive a better reception. In an effort to burnish Windows' reputation and pave the way for the next version, the company recently launched a $300 million ad campaign starring Jerry Seinfeld, Bill Gates, and a host of ordinary PC users. The ads make no mention of Vista.

Microsoft, however, has warned that Windows 7 and Vista share the same basic architecture. As a result, applications that aren't compatible with Vista won't likely run on Windows 7, either.

Microsoft shares were off 2.7% to $22.60 in mid-day trading Wednesday as world financial markets continued their downward slide.