All my purchased itunes songs are on my Q and it was very easy getting it there:
1) YOU MUST ELIMINATE PROTECTION FROM THE ITUNES MP4 FILES
The freeware I use to do this is QT Fair Use (latest version is 2.5)
You can get a copy at the following link, but always can google this software name to find another link:
http://hymn-project.org/forums/viewtopic.php?t=1553
It's very simple - just run the program & then pick & choose any MP4 files you have once the program is installed and it takes you through the process. It's a bit time consuming, but that depends on the amount of files you have.
That should do it for the Q, but if you have another program that only reads MP3's, then eliminating the protection from the MP4 that you get from itunes with QT Fair Use will not do that for you. You will also need to download another software to convert MP4 to MP3.
2) CONVERTING ITUNES MP4 FORMAT TO MP3
You must have done the first described step first - QT eliminates the protection & you won't be able to convert if the protection is still on the file before running it through QT.
I use a Free MP3 Converter that I found through Koyote Soft:
http://www.koyotesoft.com/indexEn.html
This too is extremely simple and much quicker than eliminating the MP4 protection.
These two major steps - QT Fair Use (eliminate protection) and MP4-MP3 conversion will make your purchased itunes viewable on any system as an unprotected MP3. (simply elminating the protection from the itunes file is enough for me to listen to them all on the Q, and I only converted a few for my car's audio system to MP3.)