Despite EMI selling DRM-free songs, there is still a lot of music on the iTunes store that is protected by Apple’s Fair Play DRM software. The most obvious way to strip Fair Play is to burn your DRM-ed music onto a CD and then re-rip it, loosing some of the quality in the process.
Fortunately, MacLife has just published another two methods that are worth trying. The first requires the use of Audio Hijack ($16 from RogueAmoeba) to record the sound being played back in iTunes. The recorded file is then edited in iMovie and re-imported into iTunes.
The second method uses iMovie alone. This is simpler than the first, and does not require Audio Hijack either. Import your DRM-ed music into iMovie and then export it as an AIFF file. Once back in iTunes, you can then re-encode to MP3/AAC/Apple Lossless back in iTunes.
Note that tempering with DRM software is considered illegal in some parts of the world. Do so at your own risk.