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';
}