I use SimpleXML in PHP5 just just about everything these days. If I ever need anything extra, I can load the SimpleXMLElement in to a DOM node and vice-versa.
Looking forward to finding out all the cool stuff someone like you might be able to come with on podcast.com's data - opml, rss, allsorts - it would be pretty simple to generate any other formats and api calls you might need ;)
When I get the user reg live and also the feedback channels in place, then it could get pretty interesting quite quickly.
not long now