First, let me preface this by saying I don't use iTunes and I've never tried converting iTunes tracks to another format.
With that said, check out this article:
http://oreilly.com/pub/h/3092" onclick="window.open(this.href);return false;
The link to iOpener on that page doesn't work any more, and it seems that program is outdated anyway.
This is the latest version of a program that does the same thing:
http://dl.getdropbox.com/u/83959/myFair ... -Setup.exe" onclick="window.open(this.href);return false;
It looks like MyFairTunes7 converts the iTunes tracks into a form you can use, and then you can grab a program like the Quintessential Player mentioned, along with the MP4 import plugin. You'd import the .m4a versions of the tracks, and export them as .mp3 files.
The article says that you should back up your iTunes music located at
C:\My Documents\My Music\iTunes\iTunes Music before doing anything, just in case.
Also, while these programs are free, using them to get at the iTunes tracks and converting them like this is in a legally grey area. But there's no other way to do it, other than burning the tracks to CD and ripping them.
Somebody also left a comment saying that after using a program like MyFairTunes7, he was able to use an option within iTunes itself to convert the .m4a files to .mp3 format.
However, most of this advice is a bit old . . . Apple may have changed something to prevent this technique from working, in the meantime. You'd have to try it to find out. I'm reading that anything newer than iTunes 7.5 probably won't work.
You also might want to check this out:
http://lifehacker.com/358658/strip-drm- ... oubletwist" onclick="window.open(this.href);return false;
But DoubleTwist seems to have magically disappeared off the internet . . . I couldn't find it, but I didn't search too long.