function over(e) {
	e.className='on';
}
function out(e) {
	e.className='';
}

trs = document.getElementsByTagName('tr');
for (i=0;i<trs.length;i++) {
	trs[i].onmouseover = function() { over(this); }
	trs[i].onmouseout = function() { out(this); }
}