changing class

changing class

i, i want to change the class on the active link and delete the class on the other links
 
function golabel(label,hoehe) {
  if (movieIsLoaded(thisMovie(movieName))) {
    thisMovie(movieName).TGotoLabel("_level0/",label);
    $('div#header').height(hoehe);
 $('div#flashslide').height(hoehe);}obmain = document.getElementById('nav');
 




 
$('webcam').addClass("act");
 //works
 

$(this).addClass("act");
//does not works
 
$(label).addClass("act");
//does not works
 }
 
 
why does
$(this).addClass("act"); 
 not work?