A US federal judge in Seattle last week granted class-action status to a 2007 lawsuit that claimed Microsoft defrauded consumers by promoting PCs as "Vista Capable" when some could run only the most basic version of the then-still-unreleased operating system.

US District Court Judge Marsha Pechman, however, also put some limitations on the plaintiffs, blocking them, for instance, from arguing that Microsoft deceived consumers because that would require an individual determination for each person included in the class action.

Instead, said Pechman, the lawsuit may pursue a "price inflation" line of reasoning, which would argue that PC buyers paid more than they would have had not Microsoft's marketing boosted demand and increased prices of systems able to run Vista Home Basic, the lowest-priced and simplest edition.

In agreeing that the class-action suit could move forward on that basis, Pechman summarized the argument. "Plaintiffs argue that Microsoft artificially inflated demand for computers only capable of running Vista Home Basic, causing Plaintiffs to pay more for those PCs than they would have without the 'Windows Vista Capable' campaign," she wrote in her 25-page opinion. "Consumers paid for Vista capability (i.e., the computers were priced higher because of their Vista capability), but allegedly did not receive 'real' Vista capability."

The decision was a setback to Microsoft, which now faces a much larger potential pool of plaintiffs.

The original lawsuit, filed almost a year ago by Washington state resident Diane Kelley, charged Microsoft with deceptive practices in letting PC makers slap a "Vista Capable" sticker on PCs, when "a large number" of the machines would be able to run only Vista Home Basic. Kelley was later joined by a Californian, Kenneth Hansen. Together, they had requested class action status for the lawsuit in November.