Basically, when you buy music from iTunes, it comes with a copyright protection called DRM. These DRM-protected songs are locked so that they only work with Apple MP3 players. That means that if you bought a Microsoft Zune, you cannot use iTunes music.
So, what is the solution? You have to burn a CD. When you do this, the DRM is removed (because the music is converted to a non-DRM-compatible media). After you burn the CD, you can rip it to your PC as an MP3 file which no longer has DRM.
Alternatively, you can use TuneClone (
TuneClone - M4P to MP3 Converter - Convert M4P,WMA and Any Other Music Format to MP3 via virtual CD Burning ). TuneClone makes a virtual CD-ROM drive, tricking your PC into believing that you are burning a CD. Therefore, the DRM is removed without wasting a CD.
Here is a link to a tutorial using TuneClone and iTunes 8:
How to convert iTunes 8 protected AAC(M4P) music to MP3 with TuneClone Convert DRM protected iTunes M4P music to MP3