Load XML with urlstring variables

I have a flash page flipping book that I bought at activeden.  It uses an XML file to load in the images of the book to flip through.  I have created a PHP file that takes an event ID and creates a custom XML file for flash.  How do I have flash load an xml file like this?  Instead of passing:

_xmlLoader.loadXml("setup.xml");

I would like to pass:

_xmlLoader.loadXml("setup.php?id=" + eid);

That code doesn't seem to be working for me though.  Am I missing something here?