function toggleLayer( whichLayer ){  
        var elem, vis;  
        if( document.getElementById ) // this is the way the standards work    
        elem = document.getElementById( whichLayer );  
        else if( document.all ) // this is the way old msie versions work      
        elem = document.all[whichLayer];  
        else if( document.layers ) // this is the way nn4 works    
        elem = document.layers[whichLayer];  
        vis = elem.style;  // if the style.display value is blank we try to figure it out here  
        if(vis.display==''&&elem.offsetWidth!=undefined&&elem.offsetHeight!=undefined)    
        vis.display = (elem.offsetWidth!=0&&elem.offsetHeight!=0)?'block':'none';  
        vis.display = (vis.display==''||vis.display=='block')?'none':'block';
   }