Correct me if I'm wrong, but shouldn't your ipod tunes already be MP3's?
If you've loaded them from your computer, you should already have them as MP3's.
If you've converted them to AAC3 or whatever that format is that ipod allows, then you'll have to use a media converter, but check on the hard drive of your computer to see if the songs there aren't already MP3's.
If they are, you're all set.