uses

  windows, ddeman, ...

function Get_URL(Servicio: string): string;

var

  Cliente_DDE: TDDEClientConv;

  temp: PChar;      //<<---------This is new

begin

  Result := '';

  Cliente_DDE:= TDDEClientConv.Create( nil );

  with Cliente_DDE do

  begin

    SetLink( Servicio,'WWW_GetWindowInfo');

    temp := RequestData('0xFFFFFFFF');

    Result := StrPas(temp);

    StrDispose(temp);  // <<--Предотвращаем утечку памяти

    CloseLink;

  end;

  Cliente_DDE.Free;

end;

procedure TForm1.Button1Click(Sender);

begin

   showmessage(Get_URL('Netscape'));

// или

   showmessage(Get_URL('IExplore'));

end;