function initNav() {
	var navitems = document.getElementById("nav").getElementsByTagName("li");
	for( var i = 0; i < navitems.length; i++ )
	{
		if( navitems[i].className == "nav_item" ) {
			navitems[i].onmouseover = function(){this.className+="_over";}
			navitems[i].onmouseout = function(){this.className="nav_item";}
		}
	}
}