PHP managing XML file - reading and writing to the xml

[thawes]

http://www.phpbuilder.com/columns/joe20000907.php3
I have read the above great post discussing how to read/parse xml using php and display it to HTML. However what I want to know is how can I then write information back into that XML file. I am not interested in adding new nodes to the file, I want to update the existing content??

any help would be hugely appreciated

THANKS