To be able to burn your DRM copy protected songs to audio CD you will need to make a custom playlist (File > New Playlist). You can add music tracks to a playlist easily by dragging and dropping them from your music library to your newly created playlist. For instructions on how to achieve this, why not follow our tutorial on How to Create a Custom Playlist Using iTunes.
While creating a playlist, make sure that the total playing time (displayed at the bottom of the screen) doesn't exceed the capacity of the CD-R or CD-RW you are using; typically, the total playing time of a 700Mb CD is 80 minutes.
