function EnumWindowsProc(const hWnd : Longword; Param: lParam): LongBool; stdcall;
var
  Buffer: array[0..1024] of Char;
begin
  Result := True;
  GetWindowText(hWnd, Buffer, sizeof(Buffer));
  if lstrlen(Buffer) = 0 then
   begin
    exit;
   end
  else
   begin
    Form1.Memo1.Lines.Add (buffer);
   end;
end;

  {****************************************************} 

procedure TForm1.Button1Click(Sender: TObject);
var
LPARRAM : DWord;
begin
EnumWindows (@EnumWindowsProc,Integer(@LPARRAM)); ***********
end;