Eh, this can become somewhat of a process. I'm pretty sure most online vendors, including iTunes, stopped DRM protecting their files. Even then, I'm sure you have been downloading songs from iTunes long before that ever happend. On top of that, they are probably in M4P format, which would needed to be converted anyways.
If you google M4P to MP3 you will find many sources. I don't want to start linking to many pages outside the forums. I'm not sure how many songs are in your library, but if it's 1,000 or so, it will take a few hours to convert.