Error:Project Target Framework Not installed

I have a successful install of VS2010,however, I can't target any versions of the .net framework other than 4.0 and 4.0 client profile.
When I open an existing project that targets other versions of the framework I get following error.

The C# project "" is targeting
".NETFramework,Version=v2.0",which is not installed on this
machine.You must download this framework,as well as .NET
Framework 3.5,in order to open and build this project.In order to
proceed,you must select an option below.

Fixed: I need to install .NET Framework 3.5 SP1 by download
http://www.microsoft.com/downloads/en/details.aspx?FamilyID=ab99342f-5d1a-413d-8319-81da479ab0d7&displaylang=en