Several versions of the Windows SDK and earlier Platform SDKs (PSDK) are available. Generally, developers should use the most recent Windows SDK, which supports several Windows operating systems. However, some developers have development requirements that call for an earlier SDK. When deciding which release of the Windows SDK to use, consider which version of Windows you will be installing the SDK on, which version of Windows and/or the .NET Framework you are targeting, and which version of Visual Studio you are using. Use the “Which SDK is Right for Me?” table on the Windows SDK Developer Center to help determine the best choice for your needs.
The Windows SDK is the successor to the Platform SDK and the .NET Framework SDK. The Windows SDK supports development with the Win32 programming model on x86, x64, and Itanium platform architectures, and also supports development with the .NET Framework programming model. Windows SDKs include most content found in recent PSDKs plus content for the .NET Framework. The PSDKs do not include content for the .NET Framework programming model.
Karin Meier Program Manager, Windows SDK Team
The MSDN Windows SDK Developer Center is the place to find resources and links to Windows SDK products, release notes, technical articles, and more.