$('a.plus_row').each(function(e) {
	$(this).click(function(event) {
		event.preventDefault();
		var last_row = $('table.index tr:last');
		$(last_row).clone(true).insertAfter($(last_row));
	});
});

http://bettesmidler.com/code/2009-08-12.htm

Adding new table rows (with a lil' help from jQuery)

jquery

JavaScript