.NET Framework Version 3.0 Redistributable Package

The .NET Framework 3.0 adds new technologies to the .NET Framework 2.0. The .NET Framework 3.0 add four new components Windows Workflow Foundation, Windows Communication Foundation, Windows CardSpace, and Windows Presentation Foundation.
All .NET Framework 2.0 based-applications will continue to run in .NET Framework Version 3.0 also.

You have to run compatibility test if you are moving to .NET Framework Version 3.0 from .Net Framework version 1.1 or 1.0.

The .NET Framework 3.0 is installed by default on Microsoft Windows Vista. Microsoft Windows XP Home or Microsoft Windows XP Home Professional, with Service Pack 2 or later, Microsoft Windows Server 2003 family with Service Pack 1 or later supports the .NET Framework 3.0

Download .NET Framework Version 3.0