PHP Help: mailing list subscription

So, I would like to add a form to my website where people can enter their email address and they get automatically added to our mailing list. Our mailing list just requires an email sent to mailinglist-join@wherever to subscribe to. The code I have is from a friend, who has it up and working on their site. The way it works is there’s the form that goes in the page content, and bit of javascript in the header that links to a .php file. I think my problem may be that WordPress requires full address paths…so I tried putting the php file into the functions.php file so I could just call the function instead of figuring out the whole address path, but I don’t think I did it right. I guess I have to do more than copy and paste.

Anyways, I would really appreciate some help on why I can’t get the subscription thing to work.

———- HEADER ———-
‘<script type=”text/javascript”>

function GetXmlHttpObject()
{
var xmlHttp=null;
try
{
// Firefox, Opera 8.0+, Safari
xmlHttp=new XMLHttpRequest();
}
catch (e)
{
// Internet Explorer
try
{
xmlHttp=new ActiveXObject(“Msxml2.XMLHTTP”);
}
catch (e)
{
xmlHttp=new ActiveXObject(“Microsoft.XMLHTTP”);
}
}
return xmlHttp;
}
function stateChanged()
{
if (xmlHttp.readyState==4)
{
document.getElementById(“subscribed”).innerHTML = xmlHttp.responseText;
}
}
function joinSp(str)
{
xmlHttp=GetXmlHttpObject()
if (xmlHttp==null)
{
alert (“Your browser does not support AJAX!”);
return;
}
var url=”joinSPBA.php”;
url = url + “?q=” + str;
xmlHttp.onreadystatechange=stateChanged;
xmlHttp.open(“GET”,url,true);
xmlHttp.send(null);
}
</script>’

———- SEPARATE PHP FILE: joinSPBA.php ———-
‘<?php

function is_valid_address($field) {
return (ereg(‘^[a-zA-Z0-9_.-]+@[a-zA-Z0-9_.-]+$’, $field));
}

$q=$_GET[“q”];
if (is_valid_address($q)) {
$to = “prebusiness-join@lists.stanford.edu “;
$subject = “(no subject)”;
$message = “none”;
$from = “$q”;
$headers = “From: $from”;
mail($to,$subject,$message,$headers);
echo “Subscription request was sent!”;
} else {
echo “Sorry, that email address is invalid.”;
}
?>’

———- BODY/CONTENT ———-
‘<div class=”sidebar”><b>Join us!</b>
Enter your email address below and click Subscribe to join our mailing list.

<p><input type=”text” id=”emailaddress” />
<input type=”button” value=”Subscribe” onClick=”document.getElementById(‘subscribed’).innerHTML = ‘Sending request…’; joinSPBA(document.getElementById(’emailaddress’).value)” /></p>
<p id=”subscribed”></p>’