Outgoing Windows development chief James Allchin says he was being "purposefully dramatic" in a three-year-old email in which he told Bill Gates and Steve Ballmer he would buy a Mac from rival Apple were he not a Microsoft employee.

The email to Microsoft’s founder and its chief executive surfaced late last week at an Iowa antitrust trial against Microsoft, and also revealed that Allchin thought that development on the Windows Vista operating system had gone astray.

In a posting on the Windows Vista blog yesterday, Allchin said the email was a "rant encouraging a change to the way we were building Windows at the time. I made the comment for effect about buying a Mac if I was not working at Microsoft. Taken out of context, this comment could be confusing".

Allchin, whose email quote was confirmed as genuine and direct by PC Advisor's sister title Computerworld.com on Monday after it was posted by open-source legal website Groklaw.net, continued: "This email is nearly three years old, and I was being purposefully dramatic in order to drive home a point. The point being that we needed to change and change quickly. We did: we changed dramatically the development process that was being used and we reset the Windows Vista development project in mid-2004, essentially starting over."

Allchin, the co-president of Microsoft's platform and services division, is stepping down at the end of this year as Vista nears its 30 January shipping date to consumers. Allchin has said previously that delays in Windows Vista's arrival - it is shipping five years after Windows XP, rather than Microsoft's intended three year gap - were due to extensive rewriting of code in order to make the OS more secure and bug-free from the get-go.

Allchin was also quoted by lawyers representing Iowa consumers in their opening arguments in the case of Comes vs Microsoft Corp as saying Microsoft had "lost sight" of customers' needs. In his blog posting, Allchin said his comments were consistent with the "spirit of being self-critical" that "continues to flourish at Microsoft. Within Microsoft everyone considers it their duty to always put their convictions and our product quality ahead of everything else. That was the intent of my mail to Bill and Steve, and I consider it a great example of how this company can focus and do what's right for customers".