Unable to use POST method

Hi,

I am using POST method to post a request but received 415 erro ar. I created a method for POST , ML querry in the request editor, selected media type as XML/text, checked POST  and clicked Post query string check box and clicked on the submit request button, but the XML is not posted but i amollowing a wront step. getting 415 error. Please let me know if I am doing anything wrong.

Thanks