Script To Highlight Text Field With Radio Button Click?

I am doing donation script. Here is my script so far

<script type="text/javascript">
<!--//
function chkDonation(){
var form = document.forms[0]; // FORM NAME OR PLACE IN FORMS COLLECTION //;
var amount = form['OtherAmount']; // TARGETTED INPUT NAME ( OtherAmount ) //;
amount.style.visibility = 'hidden';
for(var i=0, input=form.getElementsByTagName('input'); i<input.length; i++){
if(input[i].type.match(/radio/i) && input[i].name.match(/DonationAmount/i)){
if(input[i].value.match(/Other/i)){
input[i].onclick = function(){
amount.style.visibility = 'visible'; .....

I have pretty much completed my script but now what I want it to do is to add more forms/field when the "Other" radio button is selected. So when the Other button is checked, I want the script to display more fields/forms below. Only when the "other" button is selected. When "other" selected the script should display fields like "cheque", "cash", "Payment" etc.