AJAX data in XML

I am not entirely sure but I am thinking ajax is the best way to do this, but anyway here is the question.

I have to create a comment system, I am putting all the data in either 1 or several XML documents and using ajax I need to have expandanding a) comment <div> with the data and then in that more expandable components including data stored in .xml files, is this possible? if so, could you give me some tips.

Thanks in advance.