When Microsoft released Windows Vista to business customers in Europe on 30 November, it offered an extra version of the operating system to comply with the European Commission's antitrust ruling against the company.

In its 2004 decision the commission ordered Microsoft to release additional versions of Windows that come without its Windows Media Player software. The idea was to prevent Microsoft's dominance in the desktop operating system market from giving it an unfair advantage over rivals like RealNetworks and Apple.

That resulted in versions of Windows XP called "Edition N", which sold for the same price as the standard Windows XP. With the release of Windows Vista Microsoft is having to do the same again.

The company is still working with the commission to determine exactly how many N versions are required, but it expects to offer them for both home and business users, says Thor Windham-Wright, a spokesman with Microsoft's public relations agency.

"To comply with the ruling, Microsoft will have to produce an Edition N for all future editions of Windows," confirms Tom Brookes, Microsoft's spokesman in Brussels.

Microsoft released Windows Vista Business and Windows Vista Enterprise to its volume licensing customers on 30 November, along with Exchange Server 2007, its email server product, and the Office 2007 productivity suite. The consumer editions of Windows Vista are due for release on 30 January.

The main advances in Vista are better security, its revamped Aero user interface and, for businesses, features to help to reduce PC management costs, Microsoft says.

Critics have noted that there has been little support from PC makers for the "N" versions of Windows, undermining the effectiveness of the commission's ruling. Most PC makers chose not to offer Windows XP PCs with Edition N, citing little interest from customers and the expense of supporting extra versions of the operating system.

The antitrust ruling also ordered Microsoft to release protocols used by its workgroup servers to allow competing software to operate more smoothly with Windows. Microsoft is not launching the server version of Vista, code-named Longhorn until late 2007, so the company does not have to submit the protocol information for it yet.

"Documentation for Vista workgroup server products would be needed when they do launch a Vista server system, but we don’t require documentation from the Vista PC OS," Todd says.

If rival software manufacturers are unhappy about Vista’s impact on competition and complain to the European competition regulator, Todd says the commission would consider their complaints "on their merits".

It is hard to predict how the coming months will proceed with Microsoft's competitors and the commission, says Michael Silver, research vice president with analyst firm Gartner. "I think as long as Microsoft is around and they're dominant they're going to attract companies that say they are being treated unfairly.”

Enterprises in Europe will probably take longer to adopt Vista than those in the US, since European companies typically use their hardware and software longer, Silver says. Gartner predicts most organisations will test Vista for 12 to 18 months before deploying the operating system widely. "Certainly, this is just a beginning," Silver says.

But Microsoft is quick to promote early adopters. Arsenal football club, whose Emirates Stadium was the venue for Microsoft’s UK Vista launch, is among those already using the new software, the software company says.

- Paul Meller in Brussels contributed to this report.