Excel: Create a column that must contain unique values in Excel 2003/XP/2000/97

Private Sub Worksheet_Change(ByVal Target As Excel.Range)

Dim LLoop As Integer
Dim LTestLoop As Integer

Dim Lrows As Integer
Dim LRange As String
Dim LChangedValue As String
Dim LTestValue As String

'Test first 200 rows in spreadsheet for uniqueness
Lrows = 200
LLoop = 1

'Check first 200 rows in spreadsheet
While LLoop <= Lrows
LChangedValue = "A" & CStr(LLoop)

If Not Intersect(Range(LChangedValue), Target) Is Nothing Then
If Len(Range(LChangedValue).Value) > 0 Then

'Test each value for uniqueness
LTestLoop = 1
While LTestLoop <= Lrows
If LLoop <> LTestLoop Then
LTestValue = "A" & CStr(LTestLoop)
'Value has been duplicated in another cell
If Range(LChangedValue).Value = Range(LTestValue).Value Then
'Set the background color to red
Range(LChangedValue).Interior.ColorIndex = 3
MsgBox Range(LChangedValue).Value & " already exists in cell A" & LTestLoop
Exit Sub
Else
Range(LChangedValue).Interior.ColorIndex = xlNone
End If

End If

LTestLoop = LTestLoop + 1
Wend

End If
End If

LLoop = LLoop + 1
Wend

End Sub