Sending multipart/formdata with jQuery.ajax

I've got a problem sending a file to a serverside PHP-script using jQuery's ajax-function.It's possible to get the File-List with $('#fileinput').attr('files') but how is it possible to send this Data to the server? The resulting array ($_POST) on the serverside php-script is 0 (NULL) when using the file-input.

I know it is possible (though I didn't find any jQuery solutions until now, only Prototye code (http://webreflection.blogspot.com/2009/03/safari-4-multiple-upload-with-progress.html)).

This seems to be relatively new, so please do not mention file upload would be impossible via XHR/Ajax, because it's definitely working.

I need the functionality in Safari 5, FF and Chrome would be nice but are not essential.

My code for now is:

$.ajax({    url: 'php/upload.php',    data: $('#file').attr('files'),    cache: false,    contentType: 'multipart/form-data',    processData: false,    type: 'POST',    success: function(data){        alert(data);    }});