function initPage(){
	var nav = document.getElementById("nav");
    if(nav){
		var _list = nav.getElementsByTagName('li');
		for(var i = 0; i < _list.length; i++){
			if(_list[i].parentNode.parentNode == nav){
				var _btn = _list[i].getElementsByTagName('a')[0];
				if(_btn) _btn.style.marginTop = (_list[i].offsetHeight - _btn.offsetHeight)/2 + 'px';
			}
		}
	}
}
if (window.addEventListener) window.addEventListener("load", initPage, false);
else if (window.attachEvent && !window.opera) window.attachEvent("onload", initPage);