Post And Recieve Xml

Hi! Guys
I am working on a project that need to POST data in XML format and the server in return send data back in XML format.

Till now i have been able to send data via POST using curl installed on the server. using the command

$data='<XMLData/>';
$data=urlencode($data);
$header="Content-type: text/xml";
passthru("curl -o temp.xml -H \"$header\" -d \"$data\" http://xyz.com");
but the problem is that it directly takes me to a page and start putting the content on the browser.
I have tried exec also but its not generating anything.

Can any body help me out on this...
I don have PHP installed with curl...
I just wan to use exec ,passthru or any other command

Any feasible reply will be Highly Appriciated

Thanks
Dinesh Upreti