iTunes allows you to import music files in a number of formats, one of which is AAC (not ACC). But if you prefer, you can choose a different format; MP3 and WAV are two possibilities.
Even if you import in AAC format, you end up with a file on your hard drive. Just because it is in a format that is less familiar to you doesn't mean you have to write it out and then read it back in (2 steps, each of which loses quality) in a more familiar format.
There are numerous applications that will do the conversion, some of them free:
http://pcsupport.about.com/od/fileextensions/tp/free-audio-converter.htm
for example. I think the ancient Winamp will do it.
Or you can use iTunes to do the conversion:
http://ipod.about.com/od/advanceditunesuse/ht/Converting-Aac-To-Mp3.htm