Writing to xml?

Hi,

I have an xml file I use for a gallery. However the client is a bit simple and cannot grasp updating the tags, so I’ve decided to build some sort of control panel that will write to the XML, i.e. you enter the image path, description and thumbnail location, submit, and the XML is written…

Can you point me in the most basic way to do this? I know kirupa is wonderful for straight to the point tutorials