It might be official now: The days of triumphant Windows releases are gone. Instead, Microsoft's next operating system is limping toward the starting line.In addition to being years late and delivering fewer breakthroughs than promised, Windows Vista is undergoing last-minute changes to try to quell complaints from competitors and antitrust regulators. The changes--to Vista's security software, Microsoft's new Web browser for Windows XP, and virtual machine software that will work with the upcoming Longhorn Server--aim to level the playing field with rivals. But they might still not be enough.

A month before Vista's release to businesses, Microsoft says it will publish new APIs that will give vendors of security software access to Windows' kernel that's comparable to what they have in XP. It's a concession by Microsoft, which originally wanted to block all access to the kernel in 64-bit Vista. Tapping into Windows' kernel helps companies including Symantec and McAfee protect PC users against some malicious software.

But those companies fired back this week. Symantec said Microsoft's plan won't restore lost functions to its products and leaves users exposed to threats. And McAfee said Microsoft still isn't cooperating despite its public statements, and that it hadn't received any code from Redmond. European Union regulators had pushed Microsoft to make the changes.

Adrien Robinson, a director in Microsoft's security technology unit, says the APIs aren't done, but they aim to restore the malware-sniffing capabilities the companies' software lost after Microsoft closed access to the kernel. "But it's a two-way street," she says--security software companies will have to make changes to their code, too.

Microsoft also made some last-minute changes to Internet Explorer 7, released yesterday for Windows XP. PC users now have greater flexibility to choose search engines other than Microsoft's as the default choice. Microsoft made the change after complaints from the European Union's antitrust arm. Search engine company Google this spring had discussed with the European Union its disagreement with Microsoft's original mechanism for assigning the search engine in IE. "It's clearly valuable real estate," says Gary Schare, director of Windows product management at Microsoft.

And this week in Brussels, Microsoft said it would make its "virtual hard disk" format for running multiple Windows and Linux apps on a single server available under a royalty-free license, and that it wouldn't enforce its patents in the area.

The European Commission, Europe's antitrust arm, fined Microsoft 280.5 million Euros in July for failing to comply with a regulatory agreement between the company and the Commission. In 2004, the Commission fined Microsoft 497 million Euros in a dispute over what the Commission ruled was Microsoft's unwillingness to share technical information about its products with competitors.