Deff,
немного сократил ваш код.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Подсветка колонок таблиц с jQuery</title>
<script src="http://code.jquery.com/jquery-latest.js"></script>
<script type="text/javascript">
$(document).ready(function () {
$('#tableone td').mouseenter(function () { //alert("A")
var tr = $(this).parent('tr');
var Col = tr.find('td').index(this);
var Span = $('#tableone tr').index(tr.get(0));
tr.find('td:lt(' + Col + ')').addClass('hover');
$('#tableone tr:lt(' + Span + ')').find('td:eq(' + Col + ')').addClass('hover');
}).mouseleave(function () {
$('#tableone td').removeClass('hover');
});
});
</script>
</head>
<body>
<style type="text/css">
body {
background-color:#f0f0f0;
}
table {
width:600px;
margin:0 auto;
font-family:Arial, Helvetica, sans-serif;
border-spacing:0px;
}
td:hover, td.betterhover, td.hover {
background-color:#c0e2ff;
box-shadow:0 0 1px #006fcd;
}
</style>
<table id="tableone">
<tbody>
<tr><td>X</td><td>-</td><td>X</td><td>X</td><td>-</td><td>-</td><td>-</td><td>-</td></tr>
<tr><td>X</td><td>-</td><td>X</td><td>X</td><td>-</td><td>-</td><td>-</td><td>-</td></tr>
<tr><td>X</td><td>-</td><td>X</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr>
<tr><td>-</td><td>-</td><td>X</td><td>-</td><td>X</td><td>X</td><td>-</td><td>X</td></tr>
<tr><td>X</td><td>-</td><td>X</td><td>X</td><td>-</td><td>-</td><td>-</td><td>X</td></tr>
<tr><td>X</td><td>-</td><td>X</td><td>X</td><td>-</td><td>-</td><td>-</td><td>X</td></tr>
<tr><td>X</td><td>X</td><td>-</td><td>X</td><td>-</td><td>X</td><td>-</td><td>X</td></tr>
<tr><td>X</td><td>X</td><td>-</td><td>X</td><td>-</td><td>-</td><td>-</td><td>-</td></tr>
<tr><td>X</td><td>X</td><td>-</td><td>X</td><td>-</td><td>-</td><td>X</td><td>-</td></tr>
<tr><td>X</td><td>-</td><td>X</td><td>-</td><td>X</td><td>-</td><td>-</td><td>-</td></tr>
<tr><td>X</td><td>-</td><td>X</td><td>X</td><td>-</td><td>-</td><td>-</td><td>-</td></tr>
<tr><td>X</td><td>X</td><td>X</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr>
</tbody>
</table>
</body>
</html>