I\'m currently working on a solution that initially contained one project (My.First.Project.Name). I\'ve installed Castle Windsor by executing:
My.First.Project.Name
The answer is, embarassingly, blindlingly simple.
The "Package Manager Console" has a drop-down titled "Default Project" in its toolbar, changing the project there to My.Second.Project.Name then allows Install-Package Castle.Windsor to install the package into the second project.
My.Second.Project.Name
Install-Package Castle.Windsor