Integration with Vista and Windows XP
It’s important to remember that the .NET Frameworks are not the operating system. This might seem like an obvious statement, but it’s one that has been largely forgotten with the release of Windows XP. Up to this point, Windows XP has been the predominant desktop OS that has leveraged the .NET Framework. Both .NET 1.x and 2.0 were designed to run on Windows XP. What was missed is that the .NET Framework is not tied to one operating system. Both .NET 1.x and 2.0 also run on Windows 2000 and Windows 2003/R2. What you can do is write an application that leverages the frameworks that will run on multiple systems.
The challenge is that, as a developer, it can be tempting to take advantage of non-framework classes specific to the OS. This has been seen with many Windows applications that allege support for the .NET Framework but leverage Windows XP–specific tools for their application to run on only one operating system. Many of these hybrid solutions will not run on Windows 2000.
.NET 3.0 is similar to the previous frameworks, in that it will run on multiple operating systems. At launch, .NET 3.0 will run on Windows XP, Windows 2003/R2, and Windows Vista. I haven’t heard any discussion about releasing .NET 3.0 for Windows 2000 or any other Windows operating system.