mp3 & m4a/mp4 MPEG-4 AAC are supported by iTunes. As for some of the older mp1/2 formats I don't know. I suspect iTunes might not support these earlier formats.

Here's some links about mp3 & mpeg audio formats: http://rfc3003.x42.com/

http://filext.com/detaillist.php?extdetail=MP3

http://www.rowatworks.com/Overview_I...t_QT_MPEG.html

http://www.mpeg.org/MPEG/MPEG-audio-player.html

http://www.mpeg.org/MPEG/audio.html

MPeg4: http://www.m4a.com/

Here's an iPod tutorial: http://www.apple.com/support/ipod/tutorial/index.html