LOS ANGELES – Microsoft Chairman Bill Gates Tuesday revealed one of the company’s worst-kept secrets by announcing Longhorn Server will officially be called Windows Server 2008.

Gates made the announcement at Microsoft’s 16th annual Windows Hardware Engineering Conference (WinHEC), but he did not shed any additional light on when the server will ship. He said the date remains “the second half of 2007.”

The date is key because it also will bring the first public beta of Microsoft’s new virtualization technology, Windows Server Virtualization (WSV). Last week, Microsoft announced the revised ship date of the WSV public beta and tied it to Longhorn and that certain features were being eliminated in the first version..

Gates introduced the Windows Server 2008 name and joked that Microsoft was going with another creative name and then made a similar crack when he showed a picture of the packaging, which looks just like the Windows Vista packaging.

Gates also used what will be his last appearance at WinHEC before he becomes a part-time employee in July 2008, to tout market acceptance of Vista, demo security and policy features on Windows Server 2008, show a range of next generation mobile devices, and demo Home Server and Windows Rally technology for creating a wireless network for sharing data and video.

Gates highlighted the fact that the recently released Beta 3 of Windows Server 2008 for the first time includes the capability to have different password policies for different users without having to control those features from separate domain controllers.

Gates also looked into the future that it said will be marked by 64-bit processors on servers, desktops and devices, an explosion in available computing form factors, natural user interfaces, unified communications and software plus services.

In addition, he said the Microsoft has shipped 40 million copies of Vista, more than double the number of XP copies shipped in its first 100 days.

“The reaction has been very strong,” Gates said. We thought Vista “would open up a new level of ambition, and that is happening,” he told the gathered hardware partners.