Need help on Javascript

Hi All,

I am working on a MOSS 2007 platform. Here what i need to do is to show or hide columns based on drop down values. I am using the below code to implement, but not able to hide or show multiple fields. Please help me resolve the same.

<script type="text/javascript">

_spBodyOnLoadFunctionNames.push("hideFieldsOnStart");

function hideFieldsOnStart() {

//hide the control at start
var control = getTagFromIdentifierAndTitle("input","TextField","hide textbox");
control.parentNode.parentNode.parentNode.style.display="none";

var control = getTagFromIdentifierAndTitle("input","TextField","Comments");
control.parentNode.parentNode.parentNode.style.display="none";


//control.parentNode.parentNode.parentNode.style.display="none";


//add an onchange event to the dropdown
getTagFromIdentifierAndTitle("select","DropDownChoice","selection").onchange = function() {ChangeEvent()};



}


function ChangeEvent()
{

//get the dropdown
var dropDown = getTagFromIdentifierAndTitle("select","DropDownChoice","selection");

//get the selected value
var option = dropDown.options[dropDown.selectedIndex].text;



//get the control
var control = getTagFromIdentifierAndTitle("input","TextField","hide textbox");





//show hide based on your condition
if(option == "yes")
{
control.parentNode.parentNode.parentNode.style.display="";

}
else if (option == "na")
{
control.parentNode.parentNode.parentNode.style.display="none";

}
else if (option == "no")
{
control.parentNode.parentNode.parentNode.style.display="none";
}}




//this gets the field based on title identifier and tagname
function getTagFromIdentifierAndTitle(tagName, identifier, title) {
 var len = identifier.length;
 var tags = document.getElementsByTagName(tagName);
 for (var i=0; i < tags.length; i++) {
 var tempString = tags[i].id;
 if (tags[i].title == title && (identifier == "" || tempString.indexOf(identifier) == tempString.length - len)) {
 return tags[i];
 }
 }
 return null;
}


</script>