type
  TForm1 = class(TForm)
    Button1: TButton;
    ComboBox1: TComboBox;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }  
  public
    { Public declarations }
  end;

{...}

procedure TForm1.FormCreate(Sender: TObject);
begin
  { tell printer to go to the default by setting
    the PrinterIndex value to -1 }
  Printer.PrinterIndex := -1;

  { make our combobox non-editable }
  ComboBox1.Style      := csDropDownList;

  { set our combobox items to the printer printers }
  ComboBox1.Items      := Printer.Printers;

  { set combobox to view the default printer
    according to printer printerindex as set above }
  ComboBox1.ItemIndex  := Printer.PrinterIndex;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  MyHandle  : THandle;
  MyDevice,
  MyDriver,
  MyPort: array [0..255] of Char;
begin
  { set printer to the selected according to the
    combobox itemendex }
  Printer.PrinterIndex := ComboBox1.ItemIndex;

  { get our printer properties }
  Printer.GetPrinter(MyDevice,
                     MyDriver,
                     MyPort,
                     MyHandle);

  { create string of exactly what WriteProfileString()
    wants to see by concat each of the above received
    character arrays }
  StrCat( MyDevice, ',');
  StrCat( MyDevice, MyDriver );
  StrCat( MyDevice, ',');
  StrCat( MyDevice, MyPort );

  { copy our new default printer into our windows ini file
    to the [WINDOWS] section under DEVICE= }
  WriteProfileString('WINDOWS',
                     'DEVICE',
                     MyDevice );

  { tell all applications that the windows ini file has
    changed, this will cause them all to recheck default
    printer }
  SendMessage(HWND_BROADCAST,
              WM_WININICHANGE,
              0,
              LongInt(pChar('windows')));
  end;
end;