something like this. Note this is not a VBA Code but VB6 you may have to make some adjustments to the syntax
Code:
Private Sub cmdSave_Click()
'conn is ADODB.Connection
'rsTemp is ADODB.Recordset
  Dim SQLtemp As String
  Dim bNameExists As Boolean
  bNameExists = True
    SQLtemp = "SELECT COUNT (*) FROM YOURTABLE WHERE NAME_OF_PERSON = '" & Me.Text1.Text & "'"
    Set rsTemp = conn.Execute(SQLtemp)
    If rsTemp.Fields(0).Value > 0 Then
      bNameExists = False
    End If
    If bNameExists = True Then
      MsgBox "Duplicate Entry"
      Exit Sub
    Else
      'continue with saving
    End If
End Sub