I have a folder with a group of 3rd dlls that I want to show up in Visual Studio. The reason being that I am using VisualSvn and I want to be able to see when these have been updated from within visual studio.
If you enable the "Show All Files" option (by either choosing it from the Project menu or clicking the icon at the top of the Solution Explorer), files not in you project will be shown in the tree, but with a white icon.
This gives you a view of the project folder, including all of the files that are not part of your project. You should then be able to see the directory containing your 3rd party dlls and its contents.