Curious about what Microsoft is up to after the Vista release this year? 

Here is what I got from a wiki source at (parts removed for brevity):

Disclamer:  This article or section contains information about scheduled or expected future product(s).  It may contain information of a speculative nature and the content may change dramatically as the product release approaches and more information becomes available.

Well, the next operating system release will likely be the server edition of “Longhorn” (product name to be finalized).  “Longhorn Server” will be the server equivalent of Windows Vista (previously also known by the codename "Longhorn"), and is likely to contain many of the same features, as well as others aimed specifically at high-end users.  It is expected that Windows Server 2007 will also ship with WinFS

After that, it’ll be the client OS’s turn again… Code named Vienna (previously known as “Blackcomb”) will be not just a major revision of Windows, but a complete departure from the way we have typically thought about interacting with a computer.

For instance, the "Start" philosophy, introduced in Windows 95, may be completely replaced by the "new interface" which was said in 1999 to be scheduled for "Vienna", before being moved to the Longhorn project, and then back to "Vienna".

The Explorer shell will be replaced in its entirety, with features such as the taskbar being replaced by a new concept based on the last 10 years of R&D at the Microsoft "VIBE" research lab. Projects such as GroupBar and LayoutBar are expected to make an appearance, allowing users to more effectively manage and keep track of their applications and documents while in use, and a new way of launching applications is expected - among other ideas, Microsoft is investigating a pie menu-type circular interface, similar in function to the dock in Mac OS X.

All non-managed code will run in a sandboxed environment where access to the "outside world" is restricted by the operating system. Access to raw sockets will be disabled from within the sandbox, as will direct access to the file system, hardware abstraction layer (HAL), and complete memory addressing. All access to outside applications, files, and protocols will be regulated by the operating system, and any malicious activity will be halted immediately. If this approach is successful, it bodes very well for security and safety, as it is virtually impossible for a malicious application to cause any damage to the system if it is locked in what is effectively a glass box.

Another interesting feature mentioned by Bill Gates is a “pervasive typing line that will recognize the sentence that you're typing in.”