function registerTopNav(menu_id){
	var menu = document.getElementById(menu_id);
	var columns = menu.getElementsByTagName('TD');
	var c = columns.length;
	for(var i = 0; i < c; i++){
		var elem = columns[i];
		elem.onmouseover = function(){
			setHover(this);
		};
		elem.onmouseout = function(){
			clearHover(this);
		};	
	}
}

function setHover(elem){
	try{
		elem.className = 'over';
		var ul = elem.getElementsByTagName('UL')[0];
		var parent_tr = elem.parentNode;
		
		ul.style.top = getAbsTop(parent_tr) + parent_tr.offsetHeight + 'px';
		ul.style.left = getAbsLeft(elem) + 'px';	
	}catch(e){}
}

function clearHover(elem){
	try{
		elem.className = '';
	}catch(e){}
}

function getAbsTop(el) {
	iPos = 0;
	while (el != null) {
		iPos += el.offsetTop;
		el = el.offsetParent;
	}
	return iPos;
}
function getAbsLeft(el) {
	iPos = 0;
	while (el != null) {
		iPos += el.offsetLeft;
		el = el.offsetParent;
	}
	return iPos;
}