Lawyers for consumers who bought Windows XP PCs in the months before Windows Vista's release tried today to persuade a federal judge to reinstate class-action status in their lawsuit over Microsoft's "Windows Vista Capable" marketing program.

After hearing arguments from Microsoft and the plaintiffs, U.S. District Judge Marsha Pechman indicated from the bench that a ruling could come early next week. The issue promises to be a turning point for the case -- determining whether it includes a handful of people or potentially thousands. 

Microsoft used the "Windows Vista Capable" marketing program in late 2006 to assure buyers of Windows XP machines that they would be able to run Vista when it came out. The lawsuit alleges that Microsoft wrongly gave that label to many Windows XP computers that couldn't run Vista's "signature" features -- leaving them unable to run the "real" Vista, the plaintiffs contend.

Microsoft says it was clear about which Windows Vista features the Windows XP machines would able to run.

Legal arguments aside, the case is best known for causing the disclosure of internal emails showing Microsoft executives complaining privately about Windows Vista, bowing to pressure from Intel to lower the requirements for the "Vista Capable" logo, and getting into hot water with H-P and others over the way the company handled Vista's development and release.

Pechman removed the class-action status last month after determining that the plaintiffs hadn't proven Microsoft's marketing campaign artificially inflated PC prices. Lawyers for the plaintiffs are now asking the judge to certify the class based on two narrower groups of PC buyers.

That new certification request was the subject of today's hearing. Microsoft told the judge that the case doesn't merit that status because of the widely varying circumstances under which people bought the machines.

Whichever way Pechman rules on that issue, it looks as the upcoming trial in the case, set for April 13, will probably be delayed.

That's because Jeffrey Thomas, a lawyer for the plaintiffs, told the judge today that they would probably take the issue to the Ninth Circuit Court of Appeals if she doesn't recertify the class. On the other hand, if the judge rules in the plaintiffs' favor on the class certification, the procedures necessary for notifying the potential class members would also require the trial to be delayed.

Stephen Rummage, a lawyer representing Microsoft in the case, told the judge that the company is nonetheless prepared to go to trial over the claims of the six named plaintiffs. Rummage expressed confidence in the company's prospects at trial.