Emails in the ongoing class-action lawsuit against Microsoft over its Vista Capable campaign have revealed the depth of animosity it caused with Microsoft partners.

A set of emails (PDF) from Richard Walker, senior vice president at HP's consumer PC unit, discuss the decision Microsoft made to downgrade the specification it classes as Vista Capable to include the Windows Device Driver Model (WDDM).

HP had spent considerable time and money setting up new systems that were WDDM compatible, and Walker's frustration was evident.

"I hope this incident isn't a foretaste of the relationship I will have with Microsoft going forward, but I can tell you that it's left a very bad taste with me and my team," he wrote in 2006.

"The decision you have made has taken away an investment we made consciously for competitive advantage knowing that some players would choose not to make the same level of investment as we did in supporting your program requirements."

It appears that Jim Allchin, a key player in the campaign at Microsoft, was also seriously annoyed by the decision.

"I am beyond upset here. This was totally mismanaged by Intel and Microsoft, " he wrote. "What a mess. Now we have an upset partner, Microsoft destroyed credibility, as well as my own credibility shot."

Allchin then wrote that he understood that the decision came from Steve Ballmer, something Ballmer denied at the time, and continues to do so.

The case hinges on claims that Microsoft knew that so-called Vista Capable PCs would only be able to run the cut down version of Vista, without the Aero interface.