5.1 to 5.2 javascript

Hi
I am trying to migrate to 5.2 in preparation to 5.3 &6.0.
I have the followoing Javascript in 5.1 that I jsut can not work out how to change into 5.2 coding for the JavaScript OnLoad event

AddScript2Postload("

document.forms.editform.value_part.onchange=function()

{

document.forms.editform.value_description.value='USE FOR MISC ONLY';

if( document.editform.value_part.value=='MISC')

document.forms.editform.value_description.disabled=false;

else

{

document.forms.editform.value_description.disabled=true;

document.forms.editform.value_description.value='xxx';

}

}
document.forms.editform.value_net_value.disabled=true;

var vv = document.editform.value_unit_price;

var ww = document.editform.value_quantity;

vv.onchange = vv.onkeyup =ww.onchange = ww.onkeyup =function() {

var qty = document.editform.value_quantity.value;

var unit = document.editform.value_unit_price.value;

document.editform.value_net_value.value =parseFloat(qty)*parseFloat(unit);}");

Can you help as this is doing my head in!
Many thanks
Will 5.3 and 6.0 be the same as 5.2 coding?
Gareth