As Microsoft prepares to release Windows Vista to manufacturing this week and make it available to corporate users at the end of the month, the debate is ratcheting up over how much money companies could save - if any - by upgrading to the new software.

For most businesses, the cost of licensing Windows is dwarfed by what it costs to manage the operating system and the applications running on their PCs. The bulk of those expenses comes from paying the salaries of IT staffers, according to analysts.

Microsoft claims that enhancements in Vista, such as tightened security, more powerful installation tools and improved central-management capabilities, will enable companies to sharply cut the amount of time it takes to maintain PCs. That should lead to big savings, the software vendor predicts.

Lee Nicholls, a senior technology adviser at Microsoft systems integrator Getronics NV, said calculating the potential total cost of ownership savings from an upgrade to Vista can be difficult. He added that operational costs likely will go up immediately after an upgrade because of the need for additional end-user support from helpdesks.

Nonetheless, Nicholls said that based on Getronics' experiences in helping 10 large companies deploy Vista for beta testing, users can save almost $320 (£170) per PC annually.

But Robert Taylor, CIO of the Fulton County government in Georgia, said he thinks that such savings estimates likely will turn out to be little more than "funny money" for organisations such as his with lots of full-time IT staffers.

"We manage 6,000 desktops and 1,500 laptops," Taylor said. "At $300 (£160) per PC per year, that should add up to $2 million (£1m) in savings. The only way we could actually save that would be to eliminate 30 people, which we're not going to do."

On the other hand, Taylor, whose staff have been testing Vista on 100 PCs for more than 18 months as part of Microsoft's Technology Adoption Program, agreed that many of Vista's capabilities will boost automation and manageability, freeing up his staff's time for more valuable projects.

For example, he pointed to Vista's beefed-up image-management service, which will let systems administrators create personalised clone backups of PC configurations and then remotely reinstall Vista and all applications on end-user systems if necessary. Taylor said his staff will be able to avoid driving to 200-plus buildings in the 530-square-mile county, which includes Atlanta, to reinstall Windows and other software.

He also applauded Vista's User Access Control feature, which strips users of administrator privileges. That should be a major deterrent to spyware problems, Taylor said. He said he plans to start rolling out Vista as soon as possible and expects the county to finish upgrading all of its PCs by the end of next year.

Gartner analyst Michael Silver said there are big "ifs" in the cost-savings picture painted by Microsoft and Getronics. For example, Silver expects many end users to resist having their software-installation privileges and other administrative rights taken away. Even if IT managers succeed in doing so, he said, it could result in more work in other areas for their staffs. "You'll have knowledge workers calling you every 10 minutes to install some piece of software," Silver warned.

In addition, many companies already use third-party security and image-management software with Windows XP, he said. With all those factors in mind, Silver said he thinks that only in the most aggressive scenarios, such as companies that upgrade unmanaged XP systems to well-managed Vista ones, will IT managers be able to realise annual savings of about $200 per PC (£105).

And that figure excludes some migration costs and the price of software licences, said Silver.