Non serve nessuna API.

codice:
 InputBox("Inserisci il tuo nome", "Info", String.Empty, Min(Me.Location.X + ((Me.Width - 369) / 2), Screen.PrimaryScreen.WorkingArea.Width - 369), Min(Me.Location.Y + ((Me.Height - 155) / 2), Screen.PrimaryScreen.WorkingArea.Height - 155))