uznik73, вот как выглядит путёвый тестовый пример...
<!DOCTYPE html>
<html>
<head>
<title>test</title>
<style type="text/css">
</style>
<script type="text/javascript">
function Get() {
var ot=document.getElementsByTagName('table')
var i=0
var val
while (ot[i]) {
if (ot[i].className!='if_ch') {
i++
continue
}
val=ot[i].rows[0].cells[1].innerHTML
alert(val)
i++
}
}
</script>
</head>
<body>
<table>
<tbody>
<tr>
<td>
<span>Test</span>
</td>
<td>100</td>
</tr>
</tbody>
</table>
<table class="if_ch">
<tbody>
<tr>
<td class="if_ch_name ">
<span title="">Уровень жизни</span>
</td>
<td class="if_ch_val ">18.4</td>
</tr>
</tbody>
</table>
<button onclick='Get()'>Get</button>
</body>
</html>