Sorry, Linux desktop fans: When it comes to desktop operating systems, it's currently a two-way race between Windows and the Mac OS. While Microsoft's market share dwarfs Apple's, the GUI diehards have kept each other busy for nearly two decades—and end users have regularly reaped the benefits of that competition, thanks to upgrades designed to top the competition's features and performance.

This week, the cross-platform debate's been hot and heavy. Is Microsoft racing to catch up to Panther, the Mac OS X upgrade due to roll out at June's Worldwide Developers Conference? Should Apple be running scared after Microsoft's demos of its Longhorn OS at last week's Windows Hardware Engineering conference?

But based on the timing of the companies' releases, the real question isn't whether Longhorn will take the hide off Panther, which sources said is due to ship in September. Instead, it's whether Longhorn be able to best Civet ... or Bengal Tiger ... or whatever feline Apple has in store for 2005.

Microsoft last week said on the record that it won't RTM (release to manufacturing) until 2005. And contrary to rumors circulating as of last year, there won't be any kind of "Shorthorn," or interim Windows release, between Windows XP and Longhorn. It's true that the Longhorn "technical preview" alpha release that Microsoft is expected to distribute at the Professional Developers Conference in October could have some kind of chilling effect on Panther. But let's face it: Panther will be going head-to-head with XP, not Longhorn. And XP shipped in 2001.

Apple has been careful not to underestimate Microsoft on the OS front. Indeed, even though Mac users have been fulsome in their praise of the features and speed of the current version, 10.2, of Mac OS X (a k a Jaguar), Apple insiders are well-aware of areas where XP is ahead of Mac OS X.

On the performance front, Apple is reportedly working to match XP's GUI responsiveness as well as launch, boot and log-in times. For features, Apple is burning the midnight oil to add capabilities that will rival Windows Terminal Services' access to multiple desktops, XP's ability to create profiles that travel with them among machines, and extensible help-system features that allow third-party developers to provide support and updates from within the OS. Add in such niceties as transparent, file system-level compression and encryption, and Apple has a sizeable task list in front of it.

Meanwhile, here's what we know (more or less) in terms of what Microsoft's promising for Longhorn - based on info Microsoft shared at WinHEC, plus tips from some of our best tattlers.