I think you can play stuff that doesn't have the DRM encryption. On the bright side, I believe that when the player goes to read those files, the information telling it to check to see if it's encrypted is in the header. There is software that rips off the headers of the files....it's a hack to get around DRM. Of course the software is for educational purchases.
So far I haven't found any music files that I couldn't get onto an MP3 player yet...one way or another.