Microsoft: Don't Mess With HP Brian Caulfield, 11.21.08, 06:00 PM EST

Watch your back, Monkey Boy. You may have messed with the wrong bunch of PC builders.

A court filing unsealed Thursday as part of a class-action lawsuit against Microsoft (nasdaq: MSFT - news - people ) revealed that Hewlett-Packard (nyse: HPQ - news - people ) Chief Executive Mark Hurd e-mailed Microsoft Chief Executive Steve Ballmer to complain about HP's "call lines being overrun," with customers struggling to upgrade to Vista. "I'm sure you're aware of this," Hurd added.

The full text of the e-mail has not yet been released, but Hurd's complaints to Ballmer are the latest signs of escalating tensions between HP and Microsoft caused by the launch of Windows Vista in 2007.

The lawsuit accuses Microsoft of slapping labels on PCs that said the machines were Vista-capable when they didn't have the processing power needed to run some of the operating system's most touted features.

E-mails released Nov. 14 as part of the case show Richard Walker, the head of HP's PC business, hinting at the customer trouble to come in a Feb, 1, 2006, e-mail to Ballmer and other members of Microsoft's management team.

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," Walker wrote. "The decision you have made has taken away an investment we made consciously for competitive advantage knowing that some players would choose not to."

That e-mail triggered panic at Microsoft. Jim Allchin, then co-president of Microsoft's platforms and services division, quickly sent a follow-up note to Ballmer. "I am beyond being upset here," he wrote.