PHP4XSPF (PHP for XML Shareable Playlist Format) is a set of classes that aims to make it as easy and understandable as possible to create XSPF files. Have a look at the XSPF site to learn more about XSPF.
In short: XSPF is an attempt to substite other playlist formats. It is an open, on XML based format easy enough for me to understand ;)
NOTE: The classes are stil in alpha and do not incorporate the full spec or even the possibility to parse a XSPF file. However the generating of a XSPF file works well enough to give an impression and its quite usable. Just check it out.
For now you can check out the Subversion archive. An automagically daily build is also available.
Projectsite at Berlios https://developer.berlios.de/projects/php4xspf/