[Update: the feed opens fine with Windows Media Player (yes, there's a WMP for the Mac. ironic?) -- it just didn't automatically open when I clicked on it. I had to download the file and open the file explicitly from within WMP. Maybe, if I have time later tonight, I'll try to get it working from iTunes. My initial attempts to do so have been unsuccessful.]
[Edit: Oops. Johnny Cash's birthday isn't until Wednesday (the 26th). If I had even checked my own Johnny Cash tribute page, I would have known that.]
