Trying to revive a case that has given Microsoft chronic headaches, lawyers for PC buyers are asking an appeals court to review a federal judge's rejection of class-action status in their long-running lawsuit over Microsoft's "Windows Vista Capable" program.

Their petition, filed late last week in the Ninth Circuit U.S. Court of Appeals, disputes U.S. District Judge Marsha Pechman's recent ruling denying class-action status in the case. The decision meant the case could proceed to trial just on the claims of the six named plaintiffs. In seeking to make the case a class action again, the appeal aims to open it back up to thousands of people.

The case focuses on the marketing program that Microsoft and PC makers used to promote sales of Windows XP machines in advance of Windows Vista's January 2007 release. The suit is best known for disclosing internal company emails in which executives privately groused about the flagship PC operating system even as they praised it publicly.

The plaintiffs claim that Microsoft wrongly gave the "Vista Capable" label to computers that couldn't run the Aero Glass interface and other key Windows Vista features. Microsoft "lowered the bar and stretched the Vista name to encompass what were only 'souped-up' XP-based PCs," lawyers for the plaintiffs write in their petition to the appeals court.

Among other arguments, the petition (PDF, 45 pages) disputes Pechman's finding that there would have been too many individual questions about the circumstances of each PC purchase to make a class action feasible. For example, it points to the "Express Upgrade" promotion that let Windows XP machines upgrade to Windows Vista at little or no cost after it came out.

It's "undisputed there was only one reason anyone participated in Microsoft's Express Upgrade program: they wanted an upgrade to Vista," the plaintiffs write in their petition. "Contrary to the District Court's decision, this is a common issue that supports class certification."

Microsoft spokesman David Bowermaster said in a statement: "We believe the court was right both times it ruled this lawsuit does not deserve class-action status. The court’s decisions are well reasoned, follow established law, and should be upheld. We look forward to presenting our case to the jury if plaintiffs elect to pursue their individual claims."

The next step will be a decision by the Ninth Circuit on whether to hear the appeal about the class-action status. Action in the lower court has been stopped pending that decision.