Microsoft chief executive Steve Ballmer has told delegates at the software giant's Most Valuable Professionals Summit in Seattle that Windows Vista is "a work in progress" and that the company is trying to learn from its mistakes.

"I think we did a lot of things right, and I think we have a lot of things we need to learn from," Ballmer told the assembled independent developers, according to the Seattle Post-Intelligencer.

The five-year development cycle for Vista had been too long, according to Ballmer, and was not something that Microsoft would be repeating.

"Can we just sort of kiss that stone and move on?" he asked. "Because it turns out many things become problematic when you have those long release cycles. We can't ever let that happen again."

Ballmer confirmed that Windows 7 will be released in 2010, but would not be drawn on whether Microsoft will extend the deadline for selling new computers running XP beyond 1 July.

"I know we are going to continue to get feedback from people on how long XP should be available," he said. "We have some opinions on that. We have expressed our views."