Need help with this..

Hi,

I have this function here:

	var AdminResponse = "";

	function parseResponse(){

		var nText = AdminResponse.getElementsByTagName('optionText');
		var nVal = AdminResponse.getElementsByTagName('optionVal');
		document.forms[0]['region'].options.length = 1;
		for (i=0; i<nText.length; i++)
			{ 
			 var nOption = document.createElement('option'); 
			 var isText = document.createTextNode(nText[i].firstChild.data); 
			 nOption.setAttribute('value',nVal[i].firstChild.data); 
			 nOption.appendChild(isText); 
			 document.forms[0]['region'].appendChild(nOption);
			}
	}

	function update(nVal){

		var AdminRequest = window.ActiveXObject ? new ActiveXObject("Microsoft.XMLHTTP") : new XMLHttpRequest();   
		AdminRequest.onreadystatechange = function()
			{
		 	 if (AdminRequest.readyState == 4)
				{
		 	 	 if (AdminRequest.status == 200)
					{
			 	 	 AdminResponse = AdminRequest.responseXML;
			 	 	 parseResponse();
					}
		 	 	 else 	{
				 	 alert('Error Update.php File '+ AdminRequest.statusText);
					}
				}
			}
		var infoStr = "?choice="+nVal;
		AdminRequest.open("GET", "Update.php"+infoStr, true);
		AdminRequest.send(null); 
	}

Code (markup):

What this does is when i select a region from a list it dynamically fills the town list with the relevant towns.

My problem is that i have 3 fields for regions and 3 towns so i need to replicate this function 3 times but don't know which bits to change.

Please can someone help me replicate this another 2 times.

Thank you in advanced.
Adam