Coming from a mac geek and an itunes vet: the ONLY way to change that AAC to mp3 is to burn it as an audio cd and then rerip the cd in mp3 format. Yes it sucks, but it's also necessary to keep the file protected. The idea is so the song cannot be freely shared on kazaa or anything of the sort. Thus, they have to try and keep it in the encoded format that they can copy protect. This only applies to PURCHASED AAC's from the store. If you downloaded an AAC over the web or accidently ripped a CD in AAC format then itunes should be able to convert with no problem.
Overall I've had nothing but great things to say about itunes on a mac, and I've reccommended it to all my pc friends, and have gotten all thanks from them and no complaints.
MatherIsGod I am not sure why you are having troubles, but it may be some problem between iTunes and your personal cd burner, or some option is not set right somewhere. The Audio cd option is what you want to shoot for, and that should for all practical purposes work, so long as you are burning the CD directly from iTunes and not a 3rd party burning app.
Stinkynutz, as I said above you must burn the CD and then rerip, that is the only option
If your friend is trying to move songs to the Rio that she bought from the store, then she is SOL as far as I know for now, because Rio doesn't support the AAC format just yet. Her best bet for now is to burn the songs and rerip them as mp3s, then transfer the file to the mp3 player. If she's trying to transfer mp3s directly to the player by dragging them out of itunes' playlist, then maybe she sould try moving the file directly. I know dragging them out of the list works on a mac, but who knows how it works on a PC.
[edit] Oh yeah, right now AFAIK the store is ONLY available in the US and nowhere else...supposedly their working on elsewhere soon...although I don't see why all of NA wasn't included. The store is still in it's infant stages and will continue to grow.
That or suffer an awful, painful, horrid death.
Hope i've helped...