iPod - iTunes does not import aac files.

I am trying to import my old Winamp library into iTunes on my Mac. The problem is that all my files I imported through Winamp, which are imported as aac. Now it is my understanding that aac should be imported into iTunes with no problem. I only say this because the iTunes on my windows partition can import them and play them. So how can I make OSX import and play aac files on itunes?