[
 If dvKunde.Table.Rows.Contains(strnrhinzu ) = True Then  ....

[
  If dvKunde.Table.Rows.Contains(strnrhinzu & strnamehinzu) = True Then  ....

[
 Public Sub KundeHinzufügen()
        Dim frmForm3 As New Form3
        Dim SQL As String
        Dim strnamehinzu = Form3.strnamehinzu
        Dim strnrhinzu As System.Object = Form3.strnrhinzu
        Dim Row As DataRowView
 
        SQL = " INSERT INTO IBSDTA.STAMMDAT(PROJEKTNR ,PROJEKTNAME) VALUES('" + _
          strnrhinzu + "', '" + strnamehinzu + "')"
        cboKundeLaden(dvKunde)
 
 
        If dvKunde.Table.Rows.Contains(strnrhinzu & strnamehinzu) = True Then  
            MsgBox("Der Kunde wurde bereits in der Liste aufgenommen.", _
              MsgBoxStyle.Information, "Info")
        Else
 
 
            Dim cmd As New OleDbCommand(SQL, OleDbConnection1)
            Try
                'Connection wird geöffnet
                OleDbConnection1.Open()
 
                cmd.ExecuteNonQuery()
 
 
            Catch ex As Exception
                MsgBox(ex.Message)
                'Connection wird geschlossen
                cboKundeLaden(dvKunde)
                OleDbConnection1.Close()
            End Try
            MsgBox("Die Kundendaten wurden gespeichert", _
              MsgBoxStyle.Information, "Info")
        End If
 
    End Sub