Upcoming.org Web Services Client.
It's aimed at php5, but you can use PHP_Compat. Also, you need XML_Serializer's XML_Unserializer, and HTTP_Request.
If you do not have either of these packages on your server, it's dead easy: download, extract, and then upload to a /PEAR/ directory. The next thing: make sure that /PEAR/ is in your include_path - use ini_set() to do it :)
Two step install:
pear install -fa XML_Serializer
pear install -f http://www.ahsonline.com.au/Upcoming/Services_Upcoming-1.1.2.tgz