Code:

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;