Ajax :: Create A Private Chat From Hacking Some Opensource Chat Room?

I am trying to create a private chat from hacking some opensource chat room.I am trying to use some basic AJAX (noobie) to insert a field into a mysql db.It is doing what I want it to do mysql wise but it also changes the url.

my site runs like this. There is a page called private.php with all the php in. private.php has a switch statement to call other pages (the default is home.php).so if a user say clicks contact the link would be private.php?mode=contact.and then in the private page the switch statement would

case "contact":
require("contact.php");
break;

so the user has searched another user and wants to chat.the url at the moment is private.php?mode=full_profile&id=101 in the full_profile.php page I have the ajax in the head and a submit form to call the ajax function.

here is the ajax code

<script language="javascript" type="text/javascript">
<!--
//Browser Support Code
function ajaxFunction(){

[code]....

now the mysql query runs fine. the problem I have is that when I click the submit the url changes to private.php?x=18&y=28 . (the x and y vales are different everytime I click the submit).can anyone tell me where the x and y values are coming from and also why the ajax function is changing the url as the whole point of using ajax is to avoid that.