Write XML File - Help Needed

[kleptos]

I have seen a few examples but nothing that helps. Here is what i am trying to do.

I want to turn this:

<?xml version="1.0" ?>
<root>
    <block>
      <item>Item 1</item>
    </block>
</root>

Into this:

<?xml version="1.0" ?>
<root>
    <block>
      <item>Item 1</item>
      <item>Item 2</item>
    </block>
</root>

and keep adding item. All the examples i have seen only write one and thats it, i need to keep adding or appending new data through to this. In my application i have a textbox and a button, i want to type something into the textbox click the button and add that to the existing xml file already there. Any help of better tutorials/samples would be much appreciated. Thanks