I've used this one before. It works. I think the download is a demo version, though.

iTunes will do it also.

If I've already got the file in iTunes as a M4A and then import it again as an MP3, any idea if iTunes will list the 2 files or overwrite the first with the second?

iTunes will not overwrite the first -- it has a different file extension so they're recognized as separate files.

Do the more recent versions of iTunes allow mp3 conversion? I've been holding off upgrading because I was under the impression that they couldn't.

It will save it as a new file and leave the old file alone.

You can't convert from one format to another in iTunes - you have to go into Preferences > Advanced > Importing and import as an MP3. Once you've done that, import the tracks that you want and select "Don't replace original" (assuming, that is, that you're importing something that's already in your library).

Must be a difference between the mac and windows version. In windows you can click on the song in the playlist and chose convert to.

I say don't convert them. m4a/aac is a standard format, and any decent audio player should support it. For example: winamp plugin (which is only needed anyway if you use winamp prior to 5.12, after that it's built-in) or foobar2000. Transcoding between formats like that just means a loss in quality for no reason.

As long as it's m4a and not m4p (i.e. without apple's DRM) then it should be fine for anyone to play.

You can't convert from one format to another in iTunes

Sure you can, TheDonF. Go to Preferences->Importing like you said, and choose whatever you want the format for your song to be. They, leave preferences and highlight the song you want to convert in your library. Then, from the pulldown menu "Advanced," choose "Convert to MP3" or whatever you set your preference for.

Sweet Zombie Jesus, chococat - I stand corrected. That's tres cool. In that case, I can feel numerous choons coming people's way from my iTunes library.
great username, btw