Under Win 6, you can use the SpoolFile function, or the Passthrough escape if the printer supports it. This is detailed in TI3 96 - Direct Commands to Printer - Passthrough/Escape available from the Borland web site. Under Win32, you should use WritePrinter. The following is an example of opening a printer and writing a raw string of data to the printer. Note that you must send the correct printer name, such as "HP LaserJet 5MP" for the function to succeed. You are also responsible for embedding any necessary control codes that the printer may require.

uses WinSpool;
procedure WriteRawStringToPrinter(PrinterName:String; S:String);
 var
   Handle: THandle;
   N: DWORD;
   DocInfo : TDocInfo ;
 begin
   if not OpenPrinter(PChar(PrinterName), Handle, nil) then
     begin
      ShowMessage('error ' + IntToStr(GetLastError));
      Exit;
     end;
   with DocInfo  do begin
     pDocName := PChar('test doc');
     pOutputFile := nil;
     pDataType := 'RAW';
   end;
   StartDocPrinter(Handle,  , @DocInfo );
   StartPagePrinter(Handle);
   WritePrinter(Handle, PChar(S), Length(S), N);
   EndPagePrinter(Handle);
   EndDocPrinter(Handle);
   ClosePrinter(Handle);
 end;
procedure TForm .Button Click(Sender: TObject);
begin
  WriteRawStringToPrinter('HP', 'Test This');
end;