function ges( p ){
        this.pos = p;//container;
    this.currentClass='current';
    this.currentLink = null;
};
    
ges.prototype={
    init:function(){
        if( !document.getElementById || !document.createTextNode ){
            return;            
        }
        
        var navId = document.getElementById( this.pos );
        
        if( !navId ){
            return;
        }
        
        var navLinks = navId.getElementsByTagName( 'a' );
        alert( navLinks.length );    
        for( var i=0; i<navLinks.length-1; i++ ){
            
            if( this.currentLink != null ){
                this.currentLink = navLinks[1];
            }
                DOMHelp.addEvent( navLinks[i], 'click', this.getTarget, false );
        }
        
        if( !this.currentLink ){
            this.currentLink = navLinks[1];
            this.showBg( this.currentLink );
        }
    },

    getTarget:function( e ){
        var tar = DOMHelp.getTarget( e );
        this.showBg( tar );
    },
    
    
    showBg:function( o ){
        DOMHelp.cssjs( 'remove', this.currentLink, ges.currentClass );
        DOMHelp.cssjs( 'add', o, this.currentClass );
        this.currentLink = o;
    }
};

        <script type="text/javascript">
        var n = new ges( 'nav' );
        DOMHelp.addEvent( window, 'load', n.init, false );
    </script>