function addLoadEvent(func) {
	var oldonload = window.onload;
	if (typeof window.onload != 'function') {
		window.onload = func;
	} else {
		window.onload = function() {
			oldonload();
			func();
		}
	}
}
function centerNav() {
	var nav = document.getElementById('mainnav');
	var ul = nav.getElementsByTagName('ul')[0];
	ul.style.width = "auto";
	ul.style.left = Math.round((860-ul.offsetWidth)/2)+"px";
}
addLoadEvent(centerNav);