Adding content to XML via PHP?

I have a working XML document that I edit manually, which in turns updates a flash site.

I want to create an online post/delete page. So I can just go to a specific site (not password protected) and just add/delete news stories from XML document.

Here is my XML code:

<?xml version='1.0' encoding='utf-8'?>
   <source id='Latest News:'>
<story><br /><b><u><a href='' target='_blank'>June 10th</a></u></b><br />Content </story>
<story><br /><b><u><a href='' target='_blank'>June 23rd</a></u></b><br />Content</story>