Few things strike fear into the heart of the information technology department the way an operation system upgrade does. It's not a new version of a familiar program, it's a change to the very way all their users' computers work. They can practically hear the support-desk phone ringing already.

It's time to confront those fears. On Thursday, Microsoft will begin shipping the latest incarnation of its Windows operating system, Windows Vista. It's been five years since its predecessor, Windows XP, was launched, and the Redmond, Wash., company hopes to see businesses and consumers upgrade their computers -- and upgrade its own fortunes.

For the non-computer-literate, the operating system is the master controller for the computer. It acts as a go-between for all your software (word processors, games, photo editors, etc.) -- and the hardware (keyboard, screen, printer, etc.). It manages simple things like the fonts used to display text on your screen, and complex things like keeping track of your files and determining what individual users are allowed to do. When you hit print, it's the OS that knows what kind of printer you have and how to make it work.

Switching to a new operating system isn't like an oil change. You notice. In the case of Vista, like Windows XP before it, the entire look of your computer changes -- fonts, icons, the desktop, everything.

But it's more than just a new design. The more important upgrades are under the hood -- the upgrades that Microsoft is hoping to convince businesses and people are worth the price and the time.

Besides Vista's look (it's called Aero), users will notice a number of new features. Finding files will be easier thanks to a built-in search feature -- type in a word from the file's name or in the document (or song title), and Vista will find the file instantly.

For home users, Vista will have a new e-mail program (goodbye, Outlook Express), as well as a built-in DVD maker and photo-management system.

Businesses will have new security features and a simplified way of installing changes and upgrades to hundreds or thousands of users at once.

Although Vista's feature list is huge, it doesn't have everyone rushing to upgrade. In some cases, businesses may not be champing at the bit when they consider the effort and time required.

That's because, while a home user may install a new OS in a few hours in the evening, a business with more than a handful of users faces a major undertaking.

Even if the installation procedure goes off without a hitch, businesses are then faced with users confronting a computer desktop that's strikingly different, and with software that doesn't look and act the way they're used to.

You can imagine the result.

Further, because the operating system is so integral to users' day-to-day work, any problems that do crop up can quickly escalate. It's not a matter of being unable to send an e-mail to Aunt Shirley; it could be a matter of a critical report not being completed.

"We'll probably load Vista on one of our test machines, do some testing, make sure all our applications work," said Tim Johnson, who works on the front lines in Roanoke's information technology department. But a full deployment? Not anytime soon.

Like many companies, the city uses a lot more than the basic off-the-shelf office software. If it's going to upgrade, it needs to know that everything -- everything -- will work properly with the new OS. If not, that means a lot more work for an already overworked IT department.

"We have to make sure all that stuff falls in place before we start deploying it," Johnson said, "Our hands are tied -- we have to have those applications working."

Finally, most businesses don't want to be pioneers; as the saying goes, they're the ones with the arrows in their backs. They'd rather wait till Vista has had a chance to show its quirks -- and Microsoft has had a chance to fix them.

Cox Communications, for example, is just now upgrading its 30,000 or so computers from Windows 2000 to Windows XP. Vista isn't a consideration, according to Todd Bailey, the company's network administrator for Roanoke.

"We found no real big advantages to going to Vista," he said. In fact, one of the few reasons the company is switching to Windows XP is that its service agreement with Microsoft for Windows 2000 is expiring at the end of the year. And for the most part, software designed for Windows will run on the Vista, XP, 2000 or even 98 versions.

And what of the security features Microsoft is touting for Vista? Not a big deal, Bailey said.

"Windows XP's firewall capability is suitable for our environment right now," he said. And while holes in XP's security seemed to pop up fairly regularly, that also meant that businesses such as Cox took matters into their own corporate hands rather than rely on Redmond. "We have other very stringent security devices in place," Bailey said.

Roanoke, too, isn't convinced that Vista's security features are worth the upgrade, especially with all the software -- commercial and homegrown -- the city runs. Weighing the options led to an obvious conclusion: Vista isn't worth it, as Johnson put it, "Not versus the potential problems it might cause."