Sending XML Objects to a php script (media-type: Application/binary) *tricky*

In a game called Trackmania United, the game constantly request informations throw a web server via a php file on their server.

URL : http://game.trackmaniaunited.com/online_game/request.php

I'm looking to get the information in order to create custom signatures with informations like rank, etc.. (no hacking involved here.. for paranos out there ^^)

When i sniff the packets, it's a typical http packet with normal header and everything.. all sent via POST method. The thing is, the media type is "application/binary" and the data is in plain text in XML format.

I'd like to know how to send an XML object in "application/binary" to a php script

I'm not expert and i need your help..

Example of XML object :
--------------------------
<root>
      <game>
            <name>TmUnited</name>
            <version>0.2.0.3</version>
            <lang>fr</lang>
      </game>
      <author>
            <login>XXXXX</login>
            <password></password>
            <key>SESS-XXXX-XXXX-XXXX-XXX</key>
      </author>
      <request>GetSubscribedGroups</request>
</root>
--------------------------

the key node is probably used like a session ID.. but that's not my problem for the moment.. :)

help anyone?