When you say "import" them, do you mean the import option in the iTunes menu? That's not what it's for from memory (I know that doesn't make much sense). Just literally drag the folder with your AAC files into iTunes and they
should import straight away. For what it's worth, I think the import option is for playlists, not files. Of course Add To Library is also what you are looking for, in the same menu, but dragging-and-dropping is easier.