Variante1: Nur für das eigene Programm, nicht systemweit 

uses printers; 
 
procedure TForm1.FormCreate(Sender: TObject); 
begin 
  listbox1.items := printer.printers; 
  listbox1.itemindex := printer.printerindex; 
end; 
 
procedure TForm1.ListBox1Click(Sender: TObject); 
if listbox1.items.count > 0 then 
  printer.printerindex := listbox1.itemindex; 
end; 


// ----------------------------------------------------------- 
 
Variante2: Für den System-Drucker

uses winspool, IniFiles; 
 
var 
  pri: array of _PRINTER_INFO_2A; 
  pcbN: DWord; 
 
procedure TForm1.FormCreate(Sender: TObject); 
var 
  pcR: DWord; 
  i: integer; 
begin 
  EnumPrinters(PRINTER_ENUM_LOCAL, nil, 2, nil, 0, pcbN, pcR); 
  getmem(pri, pcbN); 
  EnumPrinters(PRINTER_ENUM_LOCAL, nil, 2, pri, pcbN, pcbN, pcR); 
  for i := 0 to pcR - 1 do 
  begin 
    listbox1.items.add(pri[i].pPrinterName); 
    if pri[i].attributes and PRINTER_ATTRIBUTE_DEFAULT <> 0 then 
      listbox1.itemindex := i; 
  end; 
end; 
 
procedure TForm1.FormDestroy(Sender: TObject); 
begin 
  freemem(pri, pcbN); 
end; 
 
procedure TForm1.ListBox1Click(Sender: TObject); 
var 
  s: string; 
  ini: TIniFile; 
begin 
  with listbox1 do 
  begin 
    if items.count > 0 then 
    begin 
      s := pri[itemindex].pPrinterName + ',' + pri[itemindex].pDriverName + 
        ',' + pri[itemindex].pPortName; 
      ini := TInifile.create('win.ini'); 
      ini.writestring('windows', 'device', s); 
      ini.free; 
      s := 'windows'; 
      SendMessage(HWND_BROADCAST, WM_SETTINGCHANGE, 0, longint(pchar(s))); 
    end; 
  end; 
end;