As I know,most of the music files downloaded from itunes are encrypted with DRM.It is a way to keep others from copy it illegally or play them in other incompatible players.So,if you want to convert itune files(mostly M4P,M4A etc) to MP3s,you just have to remove the DRM protection.
There are several methods for removing DRM:
1.CD burning and ripping,it is most commonly know.You can burn the game to a CD, and then re import it to your computer.However,it is costly(waste CDs) and fairly time consuming;
2.Use virtual CD drives instead of real CDs.Some software can do it;
3.Use software to remove DRM directly.It is cheaper and faster.And I guess there are lots of software can remove DRM,and most of them are free to try sharewares. I have just came accross a good converter through google search,you may refer to it:
http://www.google.com/search?hl=en&q=drm+removal+tools+for+drm+music+%26+videos&btnG=Google+Search&aq=f&oq=
Hope it is helpful~
ivy, January 2009