I'm hoping somebody can quickly explain importing for me.
Itunes seems to play almost every format, so I haven't paid much attention to what standard settings itunes was importing my music with.

I sadly lost my ipod and have busted out my old rio karma (only useable with a pc) from 2002. I set up the software, but then realized it was not recognizing a lot of my newer music. I looked into it and it looks as if all of the newer music was ripped (via itunes) as mp4.

I'm guessing my older software just does not recognize the newer mp4's.

I guess that when I'm importing I want to make sure I am importing in a universal format and not just in a format that may be mac specific or itunes specific.

In the itunes preferences, I looked into advanced - importing and it gives the options of AAC, AIFF, apple looseless, mp3 encoder, and WAV.

Are these the settings which determine the final file type of the imported file? What is AAC? Is that the MP4? If I chose mp3 would it import as the standard mp3. Is that outdated? Thanks for clearing this up. I'm assuming that itunes is set on the best possible output so am trusting that aac is the best...but maybe mp3 is just as good and more universal?
I do hope to get another ipod soon, so the issue isn't too big of a deal, but i would like to understand more.