I am creating a WPF form. One of the requirements is that it have a sector-based layout so that a control can be explicitly placed in one of the sectors/cells.
You're on the right track. You just need to create a Style and apply it to the ItemsControl.ItemContainerStyle. Then, in the style, specify a setter for the Grid.Row and Grid.Column. The ItemContainerStyle will get applied to the containers generated for each item.