There's plenty of threads in the forums with people who get the 'The project type is not supported by this installation' error. In fact due to a brain fart I even got it myself last week. Generally this error happens when you try to open a project written in a version of Game Studio (Express) in a version of Visual Studio that doesn't have that GS(E) installed. Most commonly because you don't have that GS(E) installed at all but one case I have seen is when you try to open a v1 file by clicking the .sln and it opens the non express version of VS. Since GS1 didn't work with VS Pro or above you can NEVER open that project unless you have express installed.

So here's how to tell which version a project is:

1. Open the project file (NOT the solution file) in notepad
2. Find the lines with <XnaFrameworkVersion> and <XnaPlatform>. This will contain v1.0, v2.0 or v3.0 and Windows, Zune or Xbox 360

In addition you can check the Project type Guid as this is what VS is checking when you get that error message

1. Find the line with <ProjectTypeGuids> ignore the 2nd GUID (FAE04EC0-301F-11D3-BF4B-00C04F79EFBC) as its always the same and represents that these project types are for C#
2. Look in the table below to find the one that matches

* These projects MUST be opened in VC# Express 2005. Sometimes even though you have 1.0 refresh installed the .sln files will open the non express version and give you the error

There are some Vista registry issues which can be fixed by reading this blog http://brianpeek.com/blog/archive/2007/11/29/weird-vista-registry-issue.aspx which on occasion also seem to cause this error message.

Thanks to Aaron for checking and adding some detail and Stephen for pointing out the very obvous verison and platform tags that I had missed!