How do I paste a macro from one spreadsheet to another.

We have a spreadsheet (97-2003) that some cells have a custom format of 0000-00-00
When you enter 1234, you get 1234-00-00 instead of 0000-12-34.
This is happening because of the following macro:

Private Sub Worksheet_Change(ByVal Target As Range)
    If Target.Cells.Count > 1 Then Exit Sub
    'modify the range A1:A20 to match your input cells
    If Not Intersect(Target, [j8:J46]) Is Nothing Then
        Application.EnableEvents = False
        Target.Value = Replace(Left(Target.Value & Space(8), 8), " ", "0")
        Application.EnableEvents = True
    End If
End Sub

How do I put this macro into a new spreadsheet to achieve the entry results?
 (I realize that the macro affects cells j8 through j46 and I will have to modify the cell range appropriately and use a macro-enabled workbook.)