> function mytest()
> {
> for (j = 0; j <= customer; j++)
> {
> var number1= document.getElementsByName("num1[]")[j].value;
> var number2 = document.getElementsByName("num2[]")[j].value;
> number1 = Number(number1);
> number2 = Number(number2);
> var result = number1 + number2;
> document.getElementsByName("total[]")[j].value = result;
> }
> }

not tested!
try:
<form name="test" id="test" .... >

....

<td>Number 1:</td><td><input type="text"
name="num[{$smarty.section.ill.index}]"
id="num[{$smarty.section.ill.index}]" /></td></tr>
<tr><td>Number 2:</td><td><input type="text"
name="num[{$smarty.section.ill.index}]" id="num[{$smarty.section.ill.index}]"/></td></tr>
<tr><td>Total:</td><td><input type="text"
name="total[{$smarty.section.ill.index}]" onBlur = "mytest()" /></td></tr>

....
....

and

function mytest()
{
t = document.getElementById(test);

for (j=0; j<=sizeof(t.num); j++)
{
number1 = Number(t.num[j].value);
number2 = Number(t.num[j+1].value);
result = number1 + number2;
t.total[j].value = result;
}
}


maybe some little modification.... and it will be work for u
no tested!