[eluser]Madmartigan1[/eluser]
There are 2 options I can think of.
Have php write (create) the xml file, or output the xml directly with php and send the proper headers.
For instance, you can have a tracklist controller, with a method that takes the filename as an argument, and echo out the appropriate xml while sending an xml header. There are a lot of ways to do this.
What have you tried so far?