Denying a Window Focus

[ghost]

I have a use case where I need to select the handle for a window (external to my app) and affirmatively keep it from gaining focus until certain conditions in my app are met. Simply forcing my app's main form to the forefront does not work since my app has other dialogs which need to get focus, obtain user input, and evaluate the input to determine that the required state exists to allow the external target window to get and keep focus.

So I guess the question is how to use WinApi in C# to "attach" to the target window and recognize when it gets focus, immediately taking focus back until the desired state in my app exists.