Is there a good way to convert my m4p to Mp3?

no, the aac/m4a is protected. itunes stopped selling protected tracks 3 years ago. i guess your m4ps predates that switch?

i used something to remove the copy protection from my purchased mp4 videos off itunes last year. ah, yes, requiem. requires you to have itunes 10.5 i believe. heh, you asked this already in 2011.