It's the hour of reckoning for Windows Vista.

After five years of course changes, false starts and a host of beta and Community Technology Preview (CTP) builds, Microsoft is set to deliver a broad-scale build of Vista to two million testers. Microsoft is likely to drop the build – known by multiple names, including the consumer Vista CTP and Vista Beta 2 – as early as this week at the Windows Hardware Engineering Conference (WinHEC) in Seattle, according to company watchers. (Around the same time, Microsoft also is likely to release Office 2007 Beta 2, the next major milestone of Microsoft's next-generation desktop suite, as well as Beta 2 of Longhorn Server.)

While the exact Vista release date is fluid, the facts are not--this cut of Vista needs to be more solid than a year's worth of previous builds from Microsoft. Even the most recent Vista builds, including two interim CTPs delivered during the past couple of months to the company's squad of elite beta testers, known as Technology Adoption Program (TAP) partners, have suffered from a variety of performance and compatibility problems, according to interviews with eight testers.

"There's too much variation in performance from one build to another," said Brandon LeBlanc, a Portland, Ore.-based Vista tester and contributor to a number of Windows community sites, including MSTechToday, LonghornBlogs and LiveSide.Net. "The changes they are continuing to make at this stage disrupt performance too much. You'd imagine they would have gotten past this stage by Beta 2."

Testers said that if the next build of Vista doesn't improve dramatically, Microsoft will have a tough time sticking to the outline the company issued in late March. Microsoft's current timeline calls for the company to release the final Vista code to manufacturing this summer or fall, allowing customers under volume-licensing agreements to get their hands on the code by November, 2006. Microsoft executives have maintained that the dual launches of Vista and Office 2007 is on for January 2007, when code for both products will be available to all customers.

Indeed, doubters of Microsoft's ability to hit its timeline aren't hard to find. Gartner in a research note earlier this month said Vista's availability could be pushed back at least by a quarter.

"Here is what any team has to get absolutely right in order to call a build Beta 2: the build has to be solid enough that testers can run it to perform their day-to-day work," said Michael Cherry, an analyst with Directions on Microsoft, based in Kirkland, Wash. "If the software is not stable enough to run in day-to-day use then it will delay testing, which delays testers finding bugs."

Sounds straightforward, but Microsoft employees and corporate testers running Vista as their primary operating system report the product is not "production-ready." Even long-time Vista testers and Windows community members, who know the intricacies of Microsoft products as well as the Redmond, Wash.-based software makers own developers and testers, are having problems with the latest builds.

While it's tricky comparison between 2001's Windows XP and Windows Vista – given the differences in the size and the complexity of the code bases– testers noted that Vista doesn't seem to be as solid and ship-ready as XP was at the Beta 2 juncture.

"With "Whistler" (Windows XP), you could basically run the OS (operating system) as a near-production based OS," said Brad Wardell, president and CEO of Stardock, Corp., a Plymouth, Mich., software vendor. "With Windows Vista, the networking issues, performance, and compatibility prevent users from making it their main OS."

Among the issues Microsoft's next build will need to address: