var state = 'none';

function showhide(layer_ref) {
    if (state == 'block') {
        state = 'none';
    } else {
        state = 'block';
    }
    
    if (document.all) { 
        eval( "document.all." + layer_ref + ".style.display = state");
    }
    
    if (document.layers) { 
        document.layers[layer_ref].display = state;
    }
    
    if (document.getElementById &&!document.all) {
        hza = document.getElementById(layer_ref);
        hza.style.display = state;
    }
}