Write XML data to existing document/tags

Subject line says it all mostly. I have an exisitng xml document that has a very simple layout I need to be able to open it and add more "point" tags - basically a user will fire up a web page and add 2 pieces of numerical data (x and y) so that the next time the xml file is read it may look like the above but with the addition e.g. I've had a look at the doco but got a bit mixed up with all the writer.WriteStartElement("title"); writer.WriteString("The Handmaid's Tale"); writer.WriteEndElement(); e.g how to say this is to be appended after the last "point" tag in an existing document not a new document and new xml structure. The aspx file will serve no other purpose than to achieve this so feel free to include all imports needed etc as there is no current document to spoil :) Cheers Jay