Im am a college student and am having trouble with the asignment and have an ass for a teacher. We need to do a code where when you click the radio button of the corresponding city it will show in the textbox what that citys zip code is. The code looks fine to me but wont display the zip code in the blank. Any suggestions?

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="XHTML namespace">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>lesson4b</title>
<script language="Javascript1.2">
<!-- hide from browsers
// Purpose: To find a zip code
// Built by: Josh Sharrer
function getzip(zipfromform)
{
var zipcodedisplay=eval(document.getzip.zipcodedisplay .value)
}
// stop hiding -->
</script>
</head>
<body>
<form id="zip codes" name="zipcode" method="post" action="">
<table width="280" border="1">
<tr>
<td width="92"><p align="right">Pick a town:</p>
<p align="right">
Elko
<input type="radio" name="radio" id="radio" value="radio" onclick=getzip(89801) />
<label for="radio"></label>
</p>
<p align="right">
Eureka
<input type="radio" name="radio" id="radio2" value="radio" onclick=getzip(89316) />
<label for="radio2"></label>
</p>
<p align="right">
Carlin
<input type="radio" name="radio" id="radio3" value="radio" onclick=getzip(89822) />
<label for="radio3"></label>
</p>
<p align="right">
Wells
<input type="radio" name="radio" id="radio4" value="radio" onclick=getzip(89804) />
<label for="radio4"></label>
</p>
<p align="right">
Wendover
<input type="radio" name="radio" id="radio5" value="radio" onclick=getzip(89883) />
<label for="radio5"></label>
</p></td>
<td width="172">Zip Code:
<label for="textfield"></label>
<input type="text" name="zipcodedisplay" id="Zip Code" /></td>
</tr>
</table>
</form>
</body>
</html>