Visual Studio 2005 with VSTA v 2.0

Because Visual Studio 2008 is not a prerequisite for the VSTA v 2.0 SDK, a VSTA 2.0 integration can be performed with Visual Studio 2005; however, the VSTA v 2.0 IDE and projects are based on Visual Studio 2008.  Therefore, like other Visual Studio 2008 project solutions (.sln files), VSTA 2.0 add-ins cannot be opened in Visual Studio 2005.  This is by design so there will be no fix. 

There is a workaround for opening some Visual Studio 2008 projects in Visual Studio 2005 - select the project file (csproj/vbproj) and choose to open it with Visual Studio 2005

                Right click on the file

                Select “Open With”

                Browse to “C:\Program Files\Microsoft Visual Studio 8\Common7\IDE\devenv.exe”

The other alternative for some VS 08 projects is to create a new VS 2005 project and add the source code from the target projects.

I do not believe the 1^st workaround works for VSTA 2.0 because the project file is dependent on Visual Studio 2008 in ways the other Visual Studio 2008 projects are not.  The 2^nd workaround will allow you to work with the project in Visual Studio 2005; however, it does not carry the VSTA and host specific project file settings and information over to the new Visual Studio 2005 project.  Some of these settings could be manually copied over by altering the properties of the Visual Studio 2005 project or copying the xml from the add-in project file to the Visual Studio 2005 project file (like build events, exe to launch on debug, debug command line arguments, and maybe the host information).