Microsoft .NET Framework 4 and .NET Framework 4 Client Profile will be made available via Windows Server Update Services. .NET Framework 4 is Microsoft's comprehensive and consistent programming model for building applications that have visually stunning user experiences, seamless and secure communication, and ability to model a range of business processes.
NET Framework 4 Client Profile provides a subset of features from .NET Framework 4. Client Profile is designed to run client apps and to enable fastest possible deployment for Windows Presentation Foundation (WPF) and Windows Forms technology.
.NET Framework 4 works side by side with older Framework versions. Apps that're based on earlier versions of the Framework will continue to run on version targeted by default.
More Info: KB829019