Targeting a Specific .NET Framework
By using Visual Studio 2008, you can specify a version of the .NET Framework for your project, .NET Framework 2.0, 3.0, or 3.5. The .NET Framework target of an application is the version of the .NET Framework that a computer must have to enable the application to run on it. Starting in Visual Studio 2008 SP1, you can also target the .NET Framework Client Profile, which is a subset of the full .NET Framework version 3.5 library.
This section contains topics that describe how to target specific versions of the .NET Framework in your projects.