[Deff]

<style>
a {
 color:#000;
}
a.active {
  border:red solid 2px;
}
</style>
<a href="http://javascript.ru/forum/">Создать форум</a><br />
<a class="xxx" href="http://lookatcode.com/showhtml">Создать форум</a>

<script type="text/javascript">
 var Link = document.URL;
 var a = document.getElementsByTagName('a');
 for(var i=0; i<a.length; i++){
   var b = a[i].getAttribute('href');
   var c = a[i].getAttribute('class'); if(!c) c='';
   if(b==Link)a[i].setAttribute('class',c+' active')
 }
</script>