Been to many sample about "autocomplete" but most pages are in PHPs. I am using my usual classic ASP code here (coupled with Ajax) and even using a Cobol COM+ object wrapper to extract data from the server. It includes three (3) files as follows;
1. ajaxPage3.ASP (main page)
2. ajaxPage3a.JS (javascript/Ajax)
3. ajaxPage3a.ASP (a page that is reading data from the server)


ajaxPage3.asp file
Code:
<%@language="vbscript" codepage="1252"%>
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<%
Dim qry, iBrand
iBrand = ""
qry = trim(request.Querystring("qFunc"))
if qry = "jxBrand" then
  iBrand = trim(request.Querystring("qBrand"))
end if
%>
<html xmlns="http://www.w3.org/1999/xhtml">
<head><title>Sample Autocomplete AJAX using Classic ASP</title>
<meta http-equiv="content-type" content="text/html; charset=us-ascii" />
<meta name="author" content="Rene Aquino Surop" />
<script type="text/javascript" src="ajaxPage3a.js"></script>
</head>
<body>
<form name="aspForm" action="ajaxPage3.asp" method="post" />
<div style="margin-top:15px; border:1px solid #3366ff; padding:10px;">
	<label for="jBrand">Car Brand: </label><div id="brandDiv" style="position:absolute; z-index:100;" /></div>&nbsp;
	<input id="txtBrand" name="txtBrand" value="<%=trim(iBrand)%>" onKeyUp="srchBrand(this.value)" />	
</div>
</form>
<div style="margin-top:15px; border:1px solid #3366ff; padding:10px;">
  The sample Autocomplete provides suggestions while you type into the field. Here the suggestions are brand names, displayed when a character are entered into the field.<br /><br />
  The datasource is a classic ASP server-side script which returns HTML data, specified via a simple URL for the source-option.
</div>
</body>
</html>

ajaxPage3a.JS file
Code:
/* car brand searching script  */
var a;
function srchBrand(varTxt){
	if(varTxt.length>0){
		var b="ajaxPage3a.asp?sid="+Math.random()+"&qAction=Search&qBrand="+varTxt; 
		a=GetXmlHttpObject(recResult);
		document.getElementById("brandDiv").style.display='';
		document.getElementById("brandDiv").innerHTML="<img src='/images/arrow.gif'/>";
		a.open("GET",b,true);a.send(null);}
	else{
		document.getElementById("brandDiv").style.display='none';
		document.getElementById("brandDiv").innerHTML="";}}

function recResult(){
	if(a.readyState==4||a.readyState=="complete"){
		document.getElementById("brandDiv").innerHTML=a.responseText;}}

/* asynchronous javascript object */
function GetXmlHttpObject(handler){
	var d=null;
	if(navigator.userAgent.indexOf("MSIE")>=0){
		var e="Msxml2.XMLHTTP";
		if(navigator.appVersion.indexOf("MSIE 5.5")>=0){
			e="Microsoft.XMLHTTP";}
		try{
			d=new ActiveXObject(e);
			d.onreadystatechange=handler;
			return d;}
		catch(e){
			alert("Browser Error. Unable to perform AJAX feature");
			return;}}
			
	if(navigator.userAgent.indexOf("Mozilla")>=0 || navigator.userAgent.indexOf("Opera")>=0){
		d=new XMLHttpRequest();
		d.onload=handler;
		d.onerror=handler;
		return d;}}

ajaxPage3a.ASP file
Code:
<%
Dim action, iBrand, iResult
action = trim(request.QueryString("qAction"))
if action = "Search" then
  iBrand = trim(request.QueryString("qBrand"))
	'this part is actually a server-side Cobol COM wrapper or object that is fetching data as below;
	'DUMMY RESULT ONLY
	iResult = "<div style='border:1px #ccc solid; margin-top:23px; margin-left:5px; width:200px;'><table width='100%' cellpadding='0px' cellspacing='0px' align='center'>"
	iResult = iResult + "<tr bgcolor='#cccc99'><td style='width:100px'><a href='ajaxPage3.asp?qFunc=jxBrand&qBrand=Chevrolet'>Chevrolet</a></td></tr>"
	iResult = iResult + "<tr bgcolor='#ffffff'><td style='width:100px'><a href='ajaxPage3.asp?qFunc=jxBrand&qBrand=Ford'>Ford</a></td></tr>"
	iResult = iResult + "<tr bgcolor='#cccc99'><td style='width:100px'><a href='ajaxPage3.asp?qFunc=jxBrand&qBrand=Honda'>Honda</a></td></tr>"
	iResult = iResult + "<tr bgcolor='#ffffff'><td style='width:100px'><a href='ajaxPage3.asp?qFunc=jxBrand&qBrand=Hyundai'>Hyundai</a></td></tr>"
	iResult = iResult + "<tr bgcolor='#cccc99'><td style='width:100px'><a href='ajaxPage3.asp?qFunc=jxBrand&qBrand=Toyota'>Toyota</a></td></tr>"
	iResult = iResult + "</table></div>"

	response.write(iResult)
end if
%>
You can also use jQuery technology here to use "autocomplete" function, it is an alternative. That is about it, but feel free to enhance it a little bit further using jQuery (must be using same entry field autocomplete function). Enjoy!