Sub TryThis()
Dim strN As String, strFirstCell As String, strLastCell As String
Dim strTopRightCell As String, strBottomLeftCell As String

strN = ActiveWindow.VisibleRange.Address
strFirstCell = Range(strN).Cells(1).Address
strLastCell = Range(strN).Cells(Range(strN).Cells.Count).Address
strTopRightCell = Cells(Range(strFirstCell).Row, Range _
(strLastCell).Column).Address
strBottomLeftCell = Cells(Range(strLastCell).Row, Range _
(strFirstCell).Column).Address

End Sub