Microsoft says it has sold 42 million volume licenses of Windows since it released Windows Vista to enterprise customers last November. But the company claims to have no statistics on how many of the corporate users who are eligible to move to Vista have actually done so.

As part of its efforts to encourage organisations to take the plunge, Microsoft late last month announced that it will ship the first service pack update of bug fixes and functionality tweaks for Vista during next year's first quarter. The SP1 release will be accompanied by a third and final service pack for Windows XP, Vista's six-year-old predecessor.

But it's no slam-dunk that SP1 will have the desired effect on Vista's corporate adoption rate, judging by the comments of IT managers such as Gregg "Skip" Bailey, CIO at the federal Bureau of Alcohol, Tobacco, Firearms and Explosives.

Bailey said his agency, which is known as the ATF, may stick with Windows XP for up to three more years, even though it plans to begin upgrading its 7,000 desktop PCs with Vista- capable hardware in January.

One of the big reasons for holding off on Vista, Bailey said, is that the ATF won't have enough time between now and January to verify that all of its applications will run effectively on the new operating system.

The ATF, which is part of the US Department of Justice, is beginning a Vista compatibility testing programme. But Bailey said that the planned desktop system replacements, which are part of the bureau's normal three-year upgrade cycle for PCs, will be finished before testing is completed.

In addition, Bailey doesn't see a compelling need to move quickly to Windows Vista. He said that although he thinks it offers advantages over Windows XP in the area of data security, the problems addressed by Vista are things "we have solved in other ways".

Another CIO who works at a Texas bank that has more than 35,000 desktops running Windows XP said he plans to hold off on Vista for "at least" another year.

"Vista adds a lot of overhead and not much benefit. Honestly, we don't see the value-add," said the CIO, who asked not to be named.

He added that his reluctance to move to Vista is out of character, given that the bank uses Microsoft software across the board and he has a personal history as an early adopter of Windows releases. For example, he moved to Windows 2000 and Windows XP when they were first released to manufacturing.

But even after Windows Vista SP1 becomes available, he expects to roll out the software to only a few developers and other users within IT. "We will probably go to Vista eventually, but we will take our time about it," the CIO said.

Microsoft can point to some budding corporate- deployment success stories for Windows Vista. David Zipkin, a senior product manager at the software vendor, said companies that should have the operating system running on at least 10,000 PCs by year's end include Citigroup, Continental Airlines and Charter Communications. The same applies to India-based IT services firms Tata Consultancy Services and Infosys Technologies, which are both Microsoft business partners, he added.

Microsoft plans to release a private beta version of SP1 to about 15,000 partners and users sometime this month. Another beta or a more fully developed "release candidate" will be distributed to a larger pool of testers later on, the company said.

IT managers typically wait to deploy the latest versions of Windows and other major Microsoft products until an SP1 update arrives because of the copious number of fixes that the new release often contains.

The SP1 release of Windows Vista is both technically and symbolically important for corporate users, said Ben Gray, an analyst at Forrester Research.

"Regardless of whether this is justified or not, experience tells desktop managers to not deploy a new Windows operating system until SP1," Gray said. He predicted that the update will spark "full-scale enterprise adoption" of Vista by the middle of next year.

Others aren't convinced of that, though.

"There are still a lot of things that need to be in Vista for the OS to really take hold," said Gartner analyst Stephen Kleynhans. He was referring partly to Microsoft's need to resolve Vista's well-publicized problems with device and software compatibility.

Zipkin contended that Microsoft has made much progress on compatibility. He said that as of last month, more than 2.2 million devices supported Vista, up from 1.5 million last November. And 2,076 applications had been certified to work with the operating system, compared with just 254 when shipments began.

But David Milman, CEO of Rescuecom, said some of the computer support centre operator's small business customers have reverted back to Windows XP because of their dissatisfaction with Vista's performance on older hardware.

"There's no question that XP is the most solid Windows platform right now," Milman said.

At the ATF, Bailey wants to have PCs in place that could handle Windows Vista when Microsoft drops mainstream support for Windows XP in April 2009, as is currently planned.

But the CIO is crossing his fingers and hoping that XP support will be extended beyond 2010. Bailey said that would enable the ATF to finish its upcoming three-year PC life cycle on XP and put off a move to Vista until the next hardware refresh.

Gregg Keizer contributed to this story.