A research note released this week from Gartner predicts that Microsoft will miss its target to ship Windows Vista on PCs by January 2007.

According to the analyst, Vista won't be broadly available to customers until the second quarter of 2007

The report, written by Gartner analysts Michael Silver, David Mitchell Smith, Stephen Kleynhans and Neil MacDonald, uses the release schedules of previous major Windows releases to prove its point.

It was 16 months between beta 2 and the release to manufacturing of Windows 2000, according to the report. That process for Windows XP took only five months, which is the same time frame Microsoft has provided for Vista. However, the development of Windows Vista for Microsoft is more on par with Windows 2000 in terms of its scope, report co-writer Smith said in an interview Tuesday.

Vista marks a major overhaul to the OS, just as Windows 2000 did when it was released, he said. This means it likely will take about nine to 12 months, not five months, for Microsoft to make Vista stable enough for final release following beta 2, Smith said.

"Windows Vista to 2000 is more of an apples to apples comparison," he said. "If you think about what XP is and was, a lot of people said [it] was, 'take Windows 2000 and make it pretty.' Most of the heavy lifting had been done with 2000. Vista is more like that."

According to Microsoft's current release schedule, Vista should be in manufacturers' hands by October, and available to business customers through its volume licensing program in late November or early December.

Microsoft has said that the final beta 2 release of Vista will come in May or June. Even if that is correct, Smith said, it still means Vista won't be released to manufacturing until at least February 2007, according to Gartner estimates.

Typically, the general release of the OS comes about two months after that, which would put Vista's general release on PCs at about April 2007 if all goes well, the report said.

Microsoft announced in March that Windows Vista would not be available on PCs in time for the busy holiday shopping season from late November to late December, as previously scheduled. Since then observers and analysts have said that if the company did not make that important target, Vista might as well be delayed into mid-2007.

In its research note, Gartner advised business customers to continue to prepare for Vista's release, but to not plan too far in advance according to Microsoft's current release dates for Vista.

"Microsoft can't accurately predict them more than a few months out, and organisations that are too reliant on Microsoft making shipment dates are leaving themselves open to excessive risk," the report warned.