So I wrote a .dll in C# (a class library project) which is called by a desktop application.
I set the Visual Studio debugger on the dll code, started the application and ...
So off to Mr. Google and the answer is that you:
* Right click on the dll project in Solution Explorer.
* Click "Properties"
* Click "Debug"
* Click "Start External Program" and then browse to the application
Now when you hit F5 (Start Debugging), Visual Studio will start the application and the dll code will breakpoint.