The same week that Microsoft discontinued support for its aged Windows 98 and Windows Millennium operating systems it rolled out thin-client software that turns older PCs into cousins of ones running Windows XP SP2.

Once code named "Eiger," the "Windows Fundamentals for Legacy PCs" software gives nearly-obsolete systems some of Windows XP's security technologies, notably Windows Firewall and Automatic Updates.

Microsoft made it clear that Fundamentals is not a true operating system. Although it's based on Windows XP Embedded SP2 it "is designed to work with the Microsoft Remote Desktop Connection client or third-party clients such as the Citrix ICA client," the company said on its Web site. Essentially, Fundamentals morphs the PC into a thin-client that runs most of its software from a server.

Fundamentals is available only to customers of Microsoft's Software Assurance (SA) volume licensing program, which gives users update rights in return for annual payments over a two- or three-year period.

The move was one of several made by Microsoft at its Worldwide Partners Conference (WWPC), which closed Thursday in Boston. Microsoft has been adding services, features, and software to SA to entice more enterprise customers. Also at WWPC, for example, Microsoft unveiled a desktop virtualization licensing plan for future users of Windows Vista Enterprise.