Microsoft and Intel have been in such a lockstep for so long in their promotion of the Windows operating system powered by x86 microprocessors that they have earned the moniker Wintel.

But when does such co-operation reach inappropriate levels?

One among a series of internal Microsoft emails, unsealed by a federal judge in a case alleging PCs labelled “Vista Capable” could not fully run its latest operating system, suggests a line may have been crossed.

In the email, dated February 26 last year, John Kalkman, a general manager handling relations with PC makers, answered why PCs using Intel’s 915 graphics chipset were allowed in 2006 to have “Vista capable” logos, when they could not run advanced features such as Vista’s 3D “Aero” interface:

“In the end, we lowered the requirement [for Vista capability] to help Intel make their quarterly earnings so they could continue to sell motherboards with the 915 graphics embedded,” he wrote.

Another Microsoft employee, Mike Ybarra, says in a 2006 email that the decision to lower the graphics requirements for the “Vista capable” logo was a mistake:

“We are caving to Intel…we are really burning HP…we are allowing Intel to drive our consumer experience,” he wrote.

Intel did have a tough year in 2006, prior to Vista going on sale at the beginning of 2007, but a company spokesman has strongly denied that Mr Kalkman could have had any knowledge of its internal financial forecasts related to chipsets and motherboards.

In another email, first reported by the Seattle Post-Intelligencer, Steven Sinofsky, the head of Windows, writes:

“Intel has the biggest challenge. Their “945″ chipset which is the baseline Vista set “barely” works right now and is very broadly used. The “915″ chipset which is not Aero capable is in a huge number of laptops and was tagged as “Vista Capable” but not Vista Premium. I don’t know if this was a good call.”

Microsoft’s response to the content of the emails is that they “reflect part of an active discussion about how best to implement the Windows Vista Capable program.” The programme was introduced in April 2006 to maintain the sales momentum of Windows XP PCs while escalating the “buzz” for the forthcoming Vista.

The class-action lawsuit alleges consumers were misled by the programme into thinking they were buying PCs that could be upgraded to the new operating system and run all of Vista’s key features. The emails reveal that retailers themselves had qualms about Microsoft lowering the technical requirements for its logo.

Microsoft could perhaps have avoided any legal action if it had taken Wal-Mart’s advice, contained in this internal memo from a Microsoft employee:

“[Wal-Mart is] extremely disappointed in the fact that the standards were lowered and feel like customer confusion will ensue. They would like to see Microsoft reconsider the program and allow for the use of 2 different logos; one that is strictly a Windows Vista Home Basic Capable [the barebones version of Vista], and the other Windows Vista Capable.”