'We believe more time is required between a stable, feature-complete Beta 2 and [release to manufacturing] to accommodate the issues expected during broad testing and allow for at least two Release Candidates,' wrote Gartner. The research firm said Microsoft will likely need at least nine to 12 months to clean up and fix bugs found in Vista after the beta 2 release, moving a final release date to between April and June 2007. Microsoft is unlikely to let Vista slip past that because of internal pressure related to financial targets surrounding its fiscal year end in June.

Microsoft asserts that it can still keep to its current schedule because it has improved upon its process for building Vista as compared with past OSes.

'The engineering and feedback processes in Windows Vista are different ' and better -- than they have been with earlier operating systems,' said Williams. 'The changes we've made have allowed us to deliver a more complete test version of the product to customers earlier than ever before and to incorporate more timely and relevant feedback faster, and they will enable us to deliver the highest quality operating system ever built.'

Delay or not, Gartner advised large companies to 'adopt managed diversity, bringing in new PCs with new OSes as early as possible, and don't upgrade established PCs.'

Companies still widely using the older Windows 2000 on the desktop should start testing beta 2 of Vista as soon as possible, wrote Gartner.