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';
}