In a decision that highlights Windows Vista's hefty system requirements, Microsoft said Tuesday that it would allow computer makers to continue to sell Windows XP on low-cost "nettop" desktop PCs for an extended period beyond the operating system's official, June 30th expiration.

Microsoft said it would allow system vendors to preload the Home edition of Windows XP on nettops through June 2010, or about one year after Windows 7 is expected to become generally available.

Microsoft defines nettops as ultra-low cost PCs that are "optimized for Internet-based activities such as e-mail, Web browsing, and instant messaging." In other words, don't expect to play Far Cry or other graphically intense games on a nettop.

The move mirrors the software maker's decision earlier this year to make Windows XP available to manufacturers of low-cost laptops beyond XP's June 30th retirement.

An example of a nettop is the Asus Eee PC, which runs Windows XP or Linux and sells for less than $400. Such low-spec machines would be incapable of running Vista.

To experience all of Vista's features, PC users need a computer with at least a 1-GHz processor, 1 GB of memory, and a 40 GB hard drive. By contrast, Windows XP Home requires only a 233-MHz processor, 64 Mbytes of RAM, and a 1.5-Gbyte disk.

Without continued access to XP, vendors like Asus would be forced to offer only Linux on their systems. It's a situation Microsoft is trying to avoid as sales of low-cost PCs rise in emerging markets like India and China.

"Customers and partners have made it clear to us that they want Windows on their netbooks and nettops," said Steven Guggenheimer, corporate vice president of the Original Equipment Manufacturer Division at Microsoft, in a statement Tuesday. "We are committed to providing Windows solutions for these devices, helping to ensure a high-quality experience for both our partners and customers," he said.

Microsoft is terminating Windows XP's availability for most PC makers on June 30, though independent system builders will have access to the OS through January, 2009. Microsoft has said it expects XP sales to account for as little as 15% of its operating system revenues in its current fiscal year, which runs through June.

Microsoft introduced Windows XP in late 2001. The company ordinarily makes operating systems available only for four years after launch date. But delays in producing Windows Vista, which debuted in January of 2007, forced Microsoft to continue selling XP longer than planned.

Microsoft originally intended to shelve Windows XP on January 30th.