Though still whistling, Microsoft's next desktop operating system is finally stepping out of the dark with this week's release of Whistler Beta 1 to a limited group of developers and hardware vendors. The successor to both its consumer-oriented Windows Millennium Edition and business-strength Windows 2000 operating systems, Whistler is due on store shelves in the second half of 2001. But Windows 95 stalwarts beware: you won't be able to simply upgrade Windows 95 machines to Whistler. Whistler's official name is still a mystery - Windows.NET and Windows 2001 are the most likely candidates. But Microsoft confirms it will ship two editions: Personal, for home users and Professional for businesses. What's more, the Personal edition will come with default interface settings and themes - a look-&-feel - that differs from Professional. Server and Embedded versions will follow. Microsoft is working to make both editions more widely compatible with games and devices from the start, unlike the Windows 2000 misstep. (Microsoft has released several updates to Windows 2000 since shipping the OS in February, to make it more compatible with certain existing applications, mostly games). The same team that created those updates is working to make Whistler even more compatible. Despite that work, Whistler is conspicuously incompatible with one popular bit of software: Windows 95. You won't be able to upgrade, although you can wipe your PC clean and install Whistler from scratch if your system can handle it. Microsoft claims most PCs still running Windows 95 are unlikely to be up to Whistler's processor and memory requirements, which are likely to exceed those of Windows 2000. For Windows 2000, Microsoft recommends a 300-MHz Pentium II processor (233 MHz for notebooks) with 64MB of memory. Whistler is intended to support 64MB systems, but 128MB of memory is recommended. On a quick look, this first beta appears to be more stable than the preliminary version of several months ago. However, Beta 1 is still nine-tenths evolution, melding Windows Me's novice-oriented add-ons with Windows 2000's more stable and secure operating system core, file system, and administrative tools. There's still room for a little revolution - Microsoft says Whistler's final function set won't be complete until Beta 2, and details of its interface won't solidify until post-Beta release candidate versions. A few nifty tools shine through even at this early stage. The Professional edition will let you dial into your office computer from home and take control of it remotely. The Personal edition won't offer that feature, but you can request help from a friend or relative and let them dial in and take control of your machine, chat, or upload files. Install Whistler Personal on a friend's computer, and you can troubleshoot her problems from the other side of the country and read her email while you're at it. Whistler Personal edition will streamline the sophisticated security, user account, and log-in features available in Whistler Professional and its Windows 2000 and NT predecessors. Although Whistler is built on the Windows 2000 kernel rather than Windows Me, Beta 1 inherits many Windows Me features. Those include Movie Maker, Media Player 7, and the Home Networking Wizard. Microsoft promises to update these bells and whistles in Beta 2 and beyond. System Restore, which tracks changes to the operating system's configuration and allows you to roll back to an earlier state, will be in Beta 2. Both versions offer a handy new feature: you can switch among user accounts (including the all-powerful Administrator account), leaving ongoing processes, such as downloads, running as background processes. A co-worker could come down and take control of the PC to check her email without interrupting your software download. Other new features include a migration wizard to move files and settings across PCs, a text-to-speech engine, and a credential manager that remembers log-in names and passwords for sites and servers you access. Certainly, it's designed to serve a variety of user interests. But whether Whistler really is to be the definitive Windows will remain unanswered until at least next summer.