"As an open-source vendor, we believe in choice," said Ram Venkataraman, director of product management for JBoss Inc. Half of JBoss' customers run Windows. And despite JBoss' acquisition by Linux vendor Red Hat Inc. earlier this year, Venkataraman said the company has no plans to cut out its Windows users.

"It's important for Java deployments to run on Windows," he said. "If you look at Web services, it's all about interoperability."

The need to interoperate and cut costs led Sherwin Lu, director of application infrastructure for Chicago-based preschool chain Le Petite Academy Inc., to upgrade to the JBoss application server on top of Windows Server 2003.

"It felt a little risky" to move to J2EE from a Visual Basic 6 environment, Lu said. But the cost of training his staff was about the same as it would have been if he had upgraded to a .Net infrastructure. Moreover, by adopting JBoss over other proprietary application servers, Lu figures he saved about a million dollars in license fees alone. And by staying on Windows, he avoided the pain and cost of "rehiring my entire sysadmin and support team."

Even Web servers -- a longtime sweet spot for the LAMP stack -- are increasingly being run on Windows.