Function TForm1.Button1Click(Sender: TObject);
var
  i: integer;
  SQLServer: Variant;
  ServerList: Variant;
begin
  List.Clear;
  try
    SQLServer := CreateOleObject('SQLDMO.Application');
    ServerList := SQLServer.ListAvailableSQLServers;
    for i := 1 to ServerList.Count do 
      ComboBox1.Items.Add(ServerList.Item(i));
  finally
    SQLServer := NULL;
    ServerList := NULL;
  end;
end;