If you want it done right, ask someone with a Mac.
1. In the
Preferences Window, Select "
Advanced."
2. Select the "
Importing" tab, and the change "
Import Using:" to "
MP3 Encoder"
3. Choose your preferred bitrate.
4. Return to the
Music Library and choose the file you want to convert. Right Click it to bring up the options menu.
5. Choose "
Convert to MP3" and watch it roll. This will create a duplicate file (one MP3, one AIFF or whatever...)
6. If you do not change your
Preferences, all CDs you import into iTunes will be MP3 from now on.