Submit form into div.

[Beffic]

So I am trying to have a form submit into a div of which the form loads into the div. I just want the data to submit now into that div. Not sure how exactly to do it, I have never done it before. So what can I do?

defaults.php

<?php
require("head.php");
if($Client['Admin']!="Yes"){
  print"You are not the administrator of this site.";
  exit;
}
if(isset($_POST['change'])){
 if($Client['Admin']!="Yes"){
   print"You are not the administrator of this site.";
   exit;
 }else{
   $Email=$_POST['Email'];
   $PhoneNumber=$_POST['PhoneNumber'];
   if(IS_NULL($Email)){
     print"Something must be put into the Email field! If none, enter \"None\".";
   }elseif(IS_NULL($PhoneNumber)){
     print"Something must be put into the Phone Number field! If none, enter \"None\".";
   }else{
     mysql_query("UPDATE `Default` SET Email='$Email', PhoneNumber='$PhoneNumber'")or die(mysql_error());
     print"Email changed to <font color=red>".$Email."</font> and phone number changed to <font color=red>".$PhoneNumber."</font>!";
   }
 }
}
$Query="SELECT * from `Default`";
$Query2=mysql_query($Query) or die(mysql_error());
while($Default=mysql_fetch_array($Query2)){
print"<h2>Default Website Settings!</h2><br />";
print"<p>Here you can change the defaults of the website. Such as the Email and Phone number that is displayed accross the website to contact you.</p>";

print"<form method=\"post\" onsubmit=\"javascript:ajaxpage('defaults.php', 'content');\">Current Email: ".$Default['Email']."<br />Current Phone Number: ".$Default['PhoneNumber']."<br /><br />New Email: <input type=\"Text\" value=".$Default['Email']." name=\"Email\"><br />New Phone Number: <input type=\"Text\" value=".$Default['PhoneNumber']." name=\"PhoneNumber\"><br /><input type=\"submit\" value=\"Change\" name=\"change\"></form>";
}

print"<br /><a class=\"regular\" href=\"javascript:ajaxpage('index.php', 'content');\">Return</a>";


?>

javascript function

function ajaxpage(url, containerid){
var page_request = false
if (window.XMLHttpRequest) // if Mozilla, Safari etc
page_request = new XMLHttpRequest()
else if (window.ActiveXObject){ // if IE
try {
page_request = new ActiveXObject("Msxml2.XMLHTTP")
} 
catch (e){
try{
page_request = new ActiveXObject("Microsoft.XMLHTTP")
}
catch (e){}
}
}
else
return false
page_request.onreadystatechange=function(){
loadpage(page_request, containerid)
}
if (bustcachevar) //if bust caching of external page
bustcacheparameter=(url.indexOf("?")!=-1)? "&"+new Date().getTime() : "?"+new Date().getTime()
page_request.open('GET', url+bustcacheparameter, true)
page_request.send(null)
}

function loadpage(page_request, containerid){
if (page_request.readyState == 4 && (page_request.status==200 || window.location.href.indexOf("http")==-1))
document.getElementById(containerid).innerHTML=page_request.responseText
}