Here's an even more efficient version of Greg's macro - with error checking:
Code:
Sub TblSort()
Application.ScreenUpdating = False
Dim r As Long, c As Long
With Selection
If .Information(wdWithInTable) = False Then Exit Sub
With .Tables(1)
.Columns.Add
c = .Columns.Count
For r = 1 To .Rows.Count
.Cell(r, c).Range.Text = r
Next
.Sort False, c, , wdSortOrderDescending
.Columns(c).Delete
End With
End With
Application.ScreenUpdating = True
End Sub