On his blog, Michael Kimsal points out a PHP4 to PHP5 XML wrapper he dig up over on this site:

I know I've looked for this sort of thing before, and I'm not sure why I didn't find it earlier, but it's just made a tedious task take about 2 minutes. Thanks guys! While I'm sure it's not perfect, it seems to be working well enough for what I needed it to do - basically read data from an XML file in to an array structure. Doesn't simplexml do that already?

The script provides a lot of the functions that PHP5 has to offer in a handy-dandy library to make working with XML in PHP4 a little easier.