How send and receive variable / php

[bogdann77]

i have the file 1.html:

.....
 <script src="/libs/jquery-1.3.1.min.js" type="text/javascript"></script>
    <script type="text/javascript">
    var url0='{$url0}';
    var url1='{$url1}';
    var url2='{$url2}';
    var url3='{$url3}';
    var OPEN_ON = false;
    openurls= function(){
    if(confirm('Opens all?') && OPEN_ON == false){
                    OPEN_ON = true;
    $.ajax({
    type: "POST",
    url: "a1.php",
    data: { url0: url0, url1: url1, url2: url2, url3: url3 },
    contentType: "application/json; charset=utf-8",
    dataType: "json",
    success: function(msg) {
      window.open(url0);
      window.open(url1);
      window.open(url2);
      window.open(url3);
alert(msg);
    },
    error: function(msg) {
alert(msg);
    }
})

                 setTimeout("location.reload(true);",3000) 

                    OPEN_ON = false
                }
                return false

    }

........
<strong><br><a href="#" onclick="openurls();return false;">Open all </a></strong>

The code from a1.php is

<?php
$url2=$_POST['url2']
    if ($url2=="http://www.yahoo.com"){
    $url2="http://google.com";
    $return = 'true';
    };
    $url3=$_POST['url3']
    if ($url3=="http://www.yahoo.com"){
    $url3="http://google.com";
    $return = 'true';
    };

    ?>

After you press the link "Open All" write "[object XMLHttpRequest]" (error).
Can anyone help me to send the four variables and after verification of a1.php, to send them back.
I am a novice with AJAX.