It seems like the plugin won't play playlist files in IE 7-8.
Even on the demo page http://sjward.org/jplayer-for-wordpress the files will buffer, but not actually play. Tracking through the timeline position updates the Current Time output, but the timeline does not actually play the audio -- even after the entire file has buffered.
The single file player works just fine.
(I was experiencing this on my own site, but then I checked the demo and saw the same problem. FWIW, on my own site I moved the enqueue scripts as recommended in the forums, but that did not correct this Internet Explorer Issue.)