Php :: Proxy To Get XML?

So I need to retrieve XML from a public API, but my app is in Flash and the public service won't implement a crossdomain.xml file. I found this PHP script online (below) for a proxy to request the URL. It works fine for URLs like:

[URL]

but the script seems to either strip or ignore any arguments on the URL, like:

[URL]

I'm PHP ignorant. Is there an easy way to have this script process those URL arguments? Here is the script:

<?php
$post_data = $HTTP_RAW_POST_DATA;
$header[] = "Content-type: text/xml";
$header[] = "Content-length: ".strlen($post_data);

[code]....