public static string GetDefaultPrinter()
 {
       string stampante = string.Empty;

       ManagementObjectSearcher searcher = new ManagementObjectSearcher("SELECT * FROM Win32_Printer");

       foreach (ManagementObject mo in searcher.Get())
       {
            if (Convert.ToBoolean(mo["Default"]))
            {
                 stampante = Convert.ToString(mo["Name"]);
                 break;
            }
       }

       return stampante;
}


public static bool SetDefault(string stampante)
{
      bool errore = false;
      int ret = 0;
      string path = "win32_printer.DeviceId='" + stampante + "'";

      using (ManagementObject printer = new ManagementObject(path))
      {
          ManagementBaseObject outParams = printer.InvokeMethod("SetDefaultPrinter", null, null);
          ret = (int)(uint)outParams.Properties["ReturnValue"].Value;
      }

      return ret == 0;
}