вот так попробуйте:
<html>
<body>
<table>
<tr>
<td class="sumItg">1</td>
<td class="test">2</td>
<td class="sumItg">2</td>
<td class="test">3</td>
<td class="sumItg">3</td>
<td class="test">4</td>
</tr>
</table>
<span id="parent"></span>
<script>
function nextElementSibling(elem)
{
if (elem.nextElementSibling)
return elem.nextElementSibling;
while (elem.nextSibling)
{
if (elem.nextSibling.nodeType == 1)
return elem.nextSibling;
elem = elem.nextSibling;
}
return null;
}
window.onload = function ()
{
var sumItg = 0;
var td = document.getElementsByTagName('td');
var i = td.length - 1;
while(i--)
{
if(td[i].className == 'sumItg')
sumItg += parseInt(td[i].innerHTML) * parseInt(nextElementSibling(td[i]).innerHTML);
}
document.getElementById('parent').innerHTML = sumItg;
}
</script>
</body>
</html>
ничего сложного нет. думайте..