• Tracks from the iTunes store don't play on my iPod
  
  Quoted from "Tracks from the iTunes store don't play on my iPod"   click to show 

  Tracks that are purchased from the iTunes store are often protected
  
  with DRM (digital rights management) protection that limits the tracks
  
  ability to be played, copied, or converted. Such tracks are usually
  
  .m4p and sometimes .m4b files.
  
  
  
  MediaMonkey can sync such files to an iPod, however, for the iPod to
  
  be able to play the tracks, the iPod must first be 'registered' to the
  
  copy of iTunes that has rights to the tracks. This 'registration' can
  
  occur either:
  
  1) When the iPod is connected to the PC for the first time while iTunes
  
  is running
  
  2) When iTunes is used to sync protected content to the device
  
  
  
  The second option is easiest in most cases:
  
  1) Run iTunes
  
  2) Plug in your device (make sure that iTunes is configured to NOT
  
  sync automatically)
  
  3) Drag and drop a DRM-protected track from the iTunes library to
  
  the device
  
  3) Close iTunes
  
  
  
  Any iTunes DRMed tracks subsequently synced with MediaMonkey
  
  should play successfully on the iPod.
• Playing M4A, M4P, M4B (AAC) Tracks
  
  Quoted from "Playing M4A, M4P, M4B (AAC) Tracks"   click to show 

  MediaMonkey 3.x supports AAC files if Quicktime is installed, though AAC encoding must be
  
  purchased as a separate option. It will play, tag, and analyze all AAC audio files, and convert
  
  all AAC tracks that don't have DRM. AAC playback in MediaMonkey 3 can fail if you've
  
  performed an upgrade from MediaMonkey 2.x to MediaMonkey 3.x, and the AAC plugins
  
  installed for MediaMonkey 2.x have not been removed--these may interfere with the native
  
  AAC plugins included with MediaMonkey 3.x.
  
  
  
  MediaMonkey 2.5 does not include AAC support at all, though playback support can be added
  
  through the use of third-party plug-ins. This support is available using the following plug-ins:
  
  1. MP4 input plugin. This supports unprotected .m4a and .mp4 files and can be downloaded from:
  
  http://www.free-codecs.com/download/...for_Winamp.htm
  
  2. Winamp MP3/MP4 input plug-ins. The MP4 plugin supports unprotected .m4a and .mp4 files
  
  and is included with Winamp 5 and can be copied to the MediaMonkey plug-ins directory
  
  (both libmp4v2.dll and in_mp4.dll must be copied). The MP3 plug-in supports AAC files.
  
  One of our users has conveniently hosted these files at:
  
  http://home.tiscali.be/ruben.castele...ore/in_mp3.dll
  
  http://home.scarlet.be/
  
  http://home.tiscali.be/ruben.castele...ore/in_mp4.dll
  
  3. M4P input plugin. This supports protected iTunes content and can be downloaded from:
  
  http://www.free-codecs.com/download/...for_Winamp.htm

If not, for all operating systems:

Current Builds
Never deal with iTunes again.

Will Rockbox be able to play songs I've bought from on-line music stores?

Quoted from GeneralFAQ < Main < [Rockbox   click to show 

Wiki]
No. It is highly unlikely that Rockbox will ever support playback of DRM encrypted audio files.

One possible option to remove DRM 'protection' is to burn the tracks to a CDR(W) and then re-rip them back into standard MP3/Ogg/etc. files using your computer. Please note that this may have legal ramifications in some jurisdictions. The Rockbox developers and community will not assist in removing DRM or in using the resulting files. If you choose to do this you are on your own.