I don't see why it needs an event structure... the simplest way is to make one VI a subVI of the other (it is up to you which way round), use the Front Panel Visible properties of the two VI's to control which one is visible at which time, and use dataflow to ensure that the functions of the main VI only execute after the configuration VI has finished. Assuming the configuration VI displays a panel of settings for the user to adjust, you are going to have to use some kind of structure to ensure you read the latest values of these when the OK button is clicked, so you might as well make it a while loop that also polls the OK button.