Here's the catch. The lyrics must be in iTunes already, as DesktopLyrics doesn't fetch them. You could use an application like GimmieSomeTune (which we've written about before) to do this, or, if you're a masochist, enter them by hand. But I've thought of a better idea.
I'm teaching myself Japanese with the fantastic podcasts at JapanesePod101.com. Something I like about them is that they embed each lesson's transcript in the file itself. So, tapping on my iPhone's screen as I listen brings up the text of the lesson.
Now, I can launch DesktopLyrics and follow along with the transcript, both the Japanese and the English translation, on my desktop as I listen. I love it. Check it out, and happy learning!