So mpeg and mp3 are not the same.
Yes, they are the same. iTunes designates mp3 as kind = 'MPEG audio file'.
So if you want to burn those on an MP3 CD, no conversion is needed.
If you convert AAC podcast audio files to mp3, they will not appear in the Podcast library, because converting kind of strips the podcast flag from them.
The converted file will then be seen as a 'normal' audio file and appear in the Music library.
Sort the Music library on 'Date Added' to quickly find them.
The native format of Audio CDs is 16 bit PCM. This format is uncompressed and MAC OS X and iTunes 'see' those files as AIFF.
AIFF is not equal to 16 bit PCM, but since both formats are uncompressed, the conversion can be done very fast.
M
17' iMac 800 MHz, 768 MB RAM, 200 GB HD, DL burner Mac OS X (10.4.8) iTunes 7.0.2