function toggleLayer( whichLayer )
{  
	var elem, vis;  
	if( document.getElementById )   
		elem = document.getElementById( whichLayer );  
	else if( document.all ) 
		elem = document.all[whichLayer];  
	else if( document.layers )    
		elem = document.layers[whichLayer];  
		vis = elem.style;  
		
	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';
}