function change_class(obj,class_name) 
{
	if (document.all) 
	{
		if(is_layer(document.all[obj]))
		{
			document.all[obj].className=class_name;
		}
	}
	else if (document.layers) 
	{
		if(is_layer(document.layers[obj]))
		{
			document.layers[obj].className=class_name;
		}
	}
	else if (document.getElementById) 
	{
		if(is_layer(document.getElementById(obj)))
		{
			document.getElementById(obj).className=class_name;
		}
	}
}