Use the following method to set the owner of a
public static void setOwner(System.Windows.Forms.Form ownerForm, System.Windows.Window window)
WindowInteropHelper helper = new WindowInteropHelper(window);
helper.Owner = ownerForm.Handle;
It might be useful when you are developing an application where you are using WinForms and WPF windows together.
Note: The window will appear always in front of its owner, I use this to display tips, for example.