function GetActiveURL(Service: String): String;
var
  DDEClient: TDDEClientConv;
  Temp: PChar;
begin
  Result:='';
  DDEClient:=TDDEClientConv.Create(nil);
  with DDEClient do
  begin
    SetLink(Service, 'WWW_GetWindowInfo');
    Temp:=RequestData('0xFFFFFFFF');
    Result:=Temp;
    StrDispose(Temp);
    CloseLink;
  end;
  DDEClient.Free;
end;

[ IExplorer ]
GetActiveURL('IExplore');

[ Netscape ]
GetActiveURL('Netscape');