uses
  WinSpool, Printers;

procedure ChangeDefaultPrinter(const Name: string);
var
  W2KSDP: function(pszPrinter: PChar): Boolean; stdcall;
  H: THandle;
  Size, Dummy: Cardinal;
  PI: PPrinterInfo2;
begin
  if (Win32Platform = VER_PLATFORM_WIN32_NT) and (Win32MajorVersion >= 5) then
  begin
    @W2KSDP := GetProcAddress(GetModuleHandle(winspl), 'SetDefaultPrinterA');
    if @W2KSDP = nil then
      RaiseLastOSError;
    if not W2KSDP(PChar(Name)) then
      RaiseLastOSError;
  end
  else
  begin
    if not OpenPrinter(PChar(Name), H, nil) then
      RaiseLastOSError;

    try
      GetPrinter(H, 2, nil, 0, @Size);
      if GetLastError <> ERROR_INSUFFICIENT_BUFFER then
        RaiseLastOSError;
      GetMem(PI, Size);
      try
        if not GetPrinter(H, 2, PI, Size, @Dummy) then
          RaiseLastOSError;
        PI^.Attributes := PI^.Attributes or PRINTER_ATTRIBUTE_DEFAULT;
        if not WinSpool.SetPrinter(H, 2, PI, PRINTER_CONTROL_SET_STATUS) then
          RaiseLastOSError;
      finally
        FreeMem(PI);
      end;
    finally
      ClosePrinter(H);
    end;
  end;
end;