Basically, it depends on what engine you're using to play the media in
question. If you have the Xine engine compiled to play Windows codecs, you
can even play MP3's. I'm running Sabayon Linux right now (great,
easy-to-install Gentoo, same portage tree), but when I used SuSe, I used to
just compile Xine myself. And according to the Wikipedia (
http://en.wikipedia.org/wiki/Advanced_Audio_Coding ), Xine can play AAC
files, and if that doesn't work, so can the Helix engine. In fact, if you
compile Amarok with mp4v2 (if your copy of TagLib supports it) you can both
read and write AAC tags.