There's more to .Net than just Microsoft's new XP brand name. Publicly, the Redmond, Wash., software giant is working overtime to pitch its new Windows XP operating system and Office XP desktop application suite as key components of its .Net software-as-a-service vision.

But privately, Microsoft is pushing equally hard, if not harder, to sell developers on an upcoming set of Web services building blocks code-named Hailstorm that could be used as part of a new offensive against America Online and its dominance in instant messaging.

Microsoft's strength is building software technologies and convincing developers to write applications and services for them. With Hailstorm, sources said Microsoft is attempting to position instant messaging as a complete development platform, rather than as a limited-purpose application.

If Microsoft succeeds, instant messaging would expand beyond being a vehicle for simple chitchat to becoming the infrastructure for a range of Web services, including Web-based e-mail, real-time stock quotations and calendar functions.

"Microsoft is using Passport and MSN Messenger combined as the new key to fight (America Online)," said one software developer briefed by Microsoft on Hailstorm. "They are turning instant messenging into an architecture."