"EnvDTE is an assembly-wrapped COM library containing the objects and members for Visual Studio core automation."
But unfortunately the implementation the the VS 2010 RTM version the library is pretty much unusable. Some methods like EnvDTE.Project.Delete() are not even implemented.
Others like EnvDTE._Solution.Remove(Project project) have buggy implementations. Removing a project with _Solution.Remove(Project project) will work, but when you try to add the same project from a different location using the _Solution.AddFromFile method you will end up with the error message "A project with that name is already opened in the solution". Once you removed it you have to restart Visual Studio if you ever want to be able to add the project to the solution.
As we speak the Visual Studio 2010 automation COM-Interface is not usable.