I put this form online so you can try the parse tree extension without installing it: http://phpaspect.org/ast. You can upload your own php script and get the xml tree or the tree visualization in png format.

I also put a mini documentation on a wiki page: http://phpaspect.org/wiki/doku.php?id=parse_tree.

Check out the main project website for all of the info surrounding the phpAspect project and where it's headed.