ajax - posterous api request with jquery only

I am trying to use jquery to interact with posterous api , however I am unable to make sense of url and how parameters will be passed . I am using this :

$.ajax({
type: 'GET',
url : 'http://posterous.com/api/2/users/me/sites',

dataType:'xml',
success: function(data,textStatus){
alert(data);
},
error: function(xhr, ajaxOptions, thrownError){
alert('XHR : ' + xhr.status);
alert("Error:"+thrownError);
}

});

});

I am sure I will have to authenticate myself to access the sites , but posterous api has'nt given any examples on how to do that , does any one have idea ?