Microsoft latest operating system, Windows Vista is likely be delayed again by at least 3 months according to research group Gartner.

The research note, released to clients on Monday, said the new Windows Vista operating system is too complex to be able to meet Microsoft's targeted November release for volume licence customers and January launch for retail consumers.

The launch of the operating system has been dogged by delays since it was first announced.

Microsoft originally targeted a 2005 launch for the new Windows, then pushed the release out to 2006 before announcing in March that Vista would again be delayed to improve the product's quality.

Although currently available as a beta, Gartner believes that the release won't be until April-June quarter of 2007 at the earliest.

"Microsoft still wants to get it out as soon as possible, but slipping from January to March is nowhere near as bad as slipping from shipping before the holidays to after the holidays", a group of Gartner analysts wrote in the report.

The news is only likely to infuriate Microsoft who insist that it was still on track to meet its launch dates.