Please help - SendAndLoad problem

Please help
I am trying to make a rss reader in flash using a php proxy to get the xml file from the external domain.
The problem I have is I wish to send a variable url called ‘url’ thats used by the php to get the xml file.

This is the Action Script I am using:

    var Sender = new LoadVars();
    var GetData = new XML();
    GetData.ignoreWhite = true;
    GetData.onLoad = function(success) {
    if (success){

    list = this.firstChild;
    len = list.childNodes.length;
list.childNodes[0].childNodes[0].firstChild.nodeValue;
 test_txt.text = list;
 test2_txt.text = len;
    //}

    }

    };
 

    theBtn.onRelease = function() {
    Sender.url="http://the/url/Iam/trying/to/get"
    Sender.sendAndLoad("proxy.php", GetData, "POST");

    };

Now I can get this to work by declaring the url directly in the php like so:

<?php 

$dataURL = "http://the/url/Iam/trying/to/get"; 

readfile($dataURL);
?> 

though I want to be able to send a variable url called ‘url’ from flash to php to use in the readfile();

Now the problem is how do I send the variable url from flash to php?
I have tried changing the php to:

<?php 
$dataURL= $_GET['url'];
readfile($dataURL);
?>

but this would not work.
I know this is an easy problem for loads of people here though so someone please help!:puzzle: