NEW WINDOWS | Glance at the surface of Longhorn, and it seems like a reinvention of fatware. The flashiest part, the Avalon graphics subsystem, is such a hog that Microsoft admits you\u2019ll need a hardware upgrade to get the full effect of its rich new 3-D GUI that will supposedly knock you out of your chair.But Avalon\u2019s pizzazz starts to seem like a diversion when you pop the hood on Longhorn and peer inside. There\u2019s so much Internet and messaging code in there, I\u2019m convinced that Microsoft has laid the foundation to end the distinction between client and server.WS-EverythingConsider the three new technology pillars that underlie Longhorn: Avalon, the WinFS storage system and Indigo. The most interesting is Indigo, a big stack of draft Web services protocols (such as WS-Security, WS-Federation, WS-ReliableMessaging, WS-Coordination and more) introduced by Microsoft and various partners that together will function as a kind of pure, Web services-based middleware with peer-to-peer functionality as well as connections to desktop apps.In other words, all Longhorn applications can be Internet applications integrated into the rest of the enterprise because the connective tissue is woven into the platform. Flip a switch, and a desktop spreadsheet, for instance, could become a Web services application. The vexing problem that has dogged the PC since birth?too much data locked in desktops?is on the verge of being solved, because every desktop will also be a server.A key element in desktops becoming good enterprise citizens is WinFS, which will stipulate an XML-based storage system for desktop data. (Contrary to rumor, WinFS doesn\u2019t replace NTFS; it runs on top of it.) This common XML denominator will make desktop content easier to expose and consume.WinFS will also help desktop applications communicate with each other. For example, why shouldn\u2019t meta-data from your e-mail client?whom you e-mail most often, the folders you browse frequently?be used to rank desktop search results? Mail clients built on WinFS and its open XML interfaces raise that possibility.XML at the CoreAre we starting to see a pattern here? XML is Longhorn\u2019s middle name. In the end, XML drives even Avalon. Along with enabling fancy 3-D tricks, Avalon comes with a new way to describe GUIs: XML application markup language (XAML?not to be confused with the old B2B play by IBM, Oracle and others known as the Transaction Authority Markup Language). Microsoft claims it learned from the simplicity of Web development and says that coding GUIs for Longhorn apps will be much easier than in earlier Windows versions. XAML also lets designers create GUIs using tools they already know. For example, Adobe has demoed an alpha version of its After Effects app that spits out XAML code.If Longhorn succeeds, XAML smart clients could eventually replace the HTML Web apps that now rule enterprise computing by default. Microsoft has long argued that browser-based apps are a step backward and should be replaced by smart, Internet-aware client applications that exploit all that excess processing power at the edge of the network (that is, desktop computers running Windows, of course). With a new technology called ClickOnce, users can download and install a "smart client" on the desktop, which then updates itself automatically as needed. Amazon has already previewed a smart 3-D shopping client that shows off this capability.So we\u2019ve come full circle. The desktop is king again, according to Microsoft?except that XML is making the physical location of desktop applications less and less important. With Avalon, WinFS and Indigo connecting Windows to everything, will it matter where applications live?