Pressured by Intel Corp., Microsoft Corp. relaxed the rules for a crucial Windows Vista marketing program -- a move that let the chip maker sell older graphics chip sets that were incapable of meeting the original requirements, internal e-mails show.

The move angered some Microsoft executives, including the then-head of Windows development, who said it would mislead customers.

In a motion unsealed Thursday in the ongoing "Windows Vista Capable" class-action lawsuit, the plaintiffs used an exchange of messages between Microsoft and Intel to back their claim that the former deceived customers who later bought machines equipped with the latter's older chip sets.

The Intel 915 chip sets -- on-the-motherboard integrated graphics that provided less-powerful graphics support than a separate graphics card -- were unable to run Aero, Vista's flashy new graphics interface. According to the e-mails, PCs using the Intel 915 chip sets initially did not qualify as Vista Capable because they could not meet the requirements of the Windows Device Driver Model (WDDM), the revamped driver architecture that debuted in Vista.

When Intel found out that Microsoft wanted to jump-start the Vista Capable campaign on April 1, 2006, three months earlier than expected, it complained to Microsoft, saying that it wouldn't have enough higher-end chip sets available to sell to computer makers.

"An April 1st date in retail means a significant change in terms of our ability to meet demand with Vista-ready parts and in short will cost us significant business," said Renee James, the Intel executive who was the primary liaison between the two firms, in a message quoted in the plaintiffs' motion. "While I do not want to discuss volume and $$ on e-mail, it is material to our business, and we do not understand Microsoft's motivation to change the previously agreed upon date."

Four days later, James dropped the name of Intel CEO Paul Otellini in another message to Will Poole, who at the time was responsible for the client version of Windows. "[Paul] doesn't understand why the date changed, and we don't accept it as just 'labels on boxes,' as the implication is these machines will be made to work someday and nobody has done any test or validation, and we do not think the potential liability of a consumer claim is a good idea."

In a filing last month, Microsoft argued that its CEO, Steve Ballmer, should not have to testify in the class-action case. However, the company acknowledged that the firms' chief executives had talked about the issue. The motion filed yesterday noted that Otellini had sent a thank-you note to Ballmer. Microsoft has denied that Ballmer had any direct involvement in the relaxing of Vista Capable requirements, saying that it was the decision of his subordinates, including Poole.