The Microsoft .NET Framework 3.0 is the new managed code programming model for Windows and the Web. Programmers can start developing managed applications with the final release of the .NET Framework 3.0.With the exception of Windows Vista (which by default includes the .NET Framework 3.0), all operating systems require you to install the .NET Framework 3.0 in order to run and develop managed applications. Some sample tools included in the Windows SDK also require you to install the .NET Framework 3.0.

The .NET Framework 3.0 Runtime components ship with Longhorn Server, but are only installed if you choose the AppServer role. Windows Longhorn Server does not include the .NET Framework 3.0 by default.

The final version of Windows Vista will be available to MSDN Subscribers (Operating System level or higher) soon. Visit MSDN Subscriptions to download Windows Vista as soon as it’s available. (Read information on purchasing an MSDN Subscription.)

Also do check out Ajax Tutorials and XML Tutorials