For the first time in five years, Microsoft Corp. is finally unveiling a new system for operating personal computers. Now the company must persuade PC buyers that the launch really matters to them.

Beginning Thursday, businesses that buy Windows licenses in bulk have first crack at the new operating system, called Vista. Consumers can get Vista on home PCs beginning Jan. 30.

Microsoft and computer vendors contend that Vista will make Windows machines more secure, powerful and graphically dynamic, especially when combined with other products Microsoft is releasing simultaneously. Those include new back-end server software for businesses, as well as Office 2007, which brings sweeping changes to widely used programs such as Word, Outlook, Excel and PowerPoint.

Much is at stake for Microsoft. Most of its revenue and almost all of its profit comes from Windows and Office, funding the company's sexier ventures in video games and music players.

But even with all the touted improvements, analysts expect Vista to only gradually emerge, especially in big organizations where upgrading can be a costly, complicated affair. Gartner Dataquest predicts that it will be 2010 before Vista outnumbers the previous operating system, Windows XP, on business computers.

A company with 10,000 employees, for example, likely has 1,000 business applications, many of which need to be tested on Vista before a company can switch its PCs to the new operating system, said Gartner analyst Michael Silver. That process often takes 12 to 18 months and lots of labor by the technology staff. (In other words, for a large business to implement Vista right away would probably require it to have been an eager-beaver type that experimented with Vista during its "beta" phase that began in mid-2005).

In the meantime, the last operating system, Windows XP, works just fine for most companies — especially with a security-enhancing patch known as Service Pack 2 that Microsoft released in 2004.

PC makers say Vista will enable computers to do things that previously were difficult or costly. For example, Lenovo Group Ltd., the world's No. 3 PC maker, says Vista greatly enhances data-backup tools it builds into its machines.

"All those capabilities are going to be one step better with Vista," said Clain Anderson, Lenovo's director of software peripherals.

But many buyers want more dramatic reasons to change their PCs.

Kamal Anand, chief technology officer for TradeStone Software Inc., a Gloucester, Mass.-based provider of supply-chain software, examined test versions of Vista and Office and found "no compelling need" to upgrade his company's 100 PCs and laptops anytime soon. Instead, Anand expects Vista and Office to slowly permeate TradeStone as it buys new PCs for employees in coming years.

"Nobody wants to go through the extra time and effort and money to upgrade an existing, well-working system," he said.

The programs in Office 2007 have been overhauled in many ways. Generally they can make it easier for people to collaborate on documents and to manage information from multiple sources. Excel in particular packs a wallop, with vastly increased number-crunching abilities. The Outlook e-mail program performs noticeably faster searches for tidbits buried in messages.

Some Office programs also have scrapped their familiar menu structure in favor of a "ribbon" atop the screen that reorders how command choices are presented to the user. While that new interface unlocks many features that were hard to find in previous generations of Office software, it will require some time to get used to, which might give tech buyers pause.

Another potential drag for Office is that the world has changed considerably since the last major release in 2003. Inexpensive, open-source alternatives to Office have gained traction. And rivals such as Google Inc. are increasingly delivering spreadsheets, word processing and other tools for free over the Internet, an attractive choice for smaller companies.

At Tabblo Inc., a Cambridge, Mass.-based startup that lets people assemble, print and share online photo collections, CEO Antonio Rodriguez expects to upgrade many, though not all, of the company's 25 PCs to Vista throughout 2007. Tabblo's staff expects Vista to make it easier to back up files and synch data over multiple computers. Rodriguez and crew also have energetically adopted Microsoft's latest Web browser, Internet Explorer 7.

But Office 2007 holds few such attractions for his company. Tabblo employees have largely abandoned Excel and Word for free programs on the Web, praising the flexibility that comes with having files stored online. Just about the only Office program Rodriguez still uses is PowerPoint for presentations.

"To me, Office 2007 is a complete non-event. I have no interest in an upgrade," he said. "Most of what I like about computing now lives online."