Coverting m4b to Mp3 in itunes

Hi,

I'm unable to convert m4b files to Mp3 on iTunes.

I can drag the m4b file into itunes and it plays on itunes on my mac but then when i view the playlist the file is in on my ipod it is not listed and does not play.

I have been told that i need to convert the m4b file to mp3 in itunes in order for it to play on the iPod.

But when I select the m4b file in itunes the convert option in the file menu is greyed out, despite going into the preferences and selecting mp3 in the import options.

Please can anyone help with this.