Originally Posted by dfkt
M4A is just one of the commonly used file extensions for AAC encoded audio files
. They can be DRMed (like WMA) and they can also be non-crippled files (also, like WMA). Of course Rockbox (or anything else besides iTunes and iPods) does not play iTunes "FairPlay" DRMed AAC files - those players only play non-crippled AAC.
What he said.
But you can make playlists with winamp, or another media player. I just use a program called "playlist creator", pretty self explanatory.