javascript onchange

I'd like to be able to add data to the field input line so that this:

<input name='input_95' id='input_2_95' type='text' value='' class='small' tabindex='37' />

becomes this:

<input name='input_95' id='input_2_95' type='text' value='' class='small' tabindex='37' onChange="CalculateTotal(this.form)" />

but only on specific fields.

The idea is populate a field using javascript:
http://www.mcfedries.com/javascript/ordertotals.asp

Any Ideas?

BTW, if anyone is curious, I was able to get After the Deadline spell checker (jquery) to work with multiple textareas.. one click checks the entire form's input and allows the writer to modify before saving the form.

for those wondering, here's a piece of code I used to make this work:

http://www.pastie.org/1357423

<script type="text/javascript">

jQuery(document).ready(function() {
   var values = $('#input_2_86,#input_2_129,#input_2_95,#input_2_96').change(function() {
   var sum = 0;
   values.each(function() { // Step through each one
   var value = parseInt($(this).val(), 10); // Retrieve its numeric value
   sum += (isNaN(value) ? 0 : value); // Add to the total
   });
  $('#input_2_88').val(sum / 4); // And show the average
  });
});
</script>