Research analysts at Gartner expect Microsoft’s Vista OS won't be widely available until the second quarter of 2007.

Gartner analysts Michael Silver, David Mitchell Smith, Stephen Kleynhans and Neil MacDonald use the release schedules of previous major Windows releases to prove their 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.

Microsoft's claims 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.

In its research note, Gartner advised business customers to continue to prepare for Vista's release: "Microsoft can't accurately predict the release 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.