M4B audiobook convert to multiple MP3's

[freakyhair]

Hi, I have an audiobook in M4B form (with bookmarks), and would like to listen to it on my Creative Zen, but the Zen doesn't accept M4B. Is there a free SW that converts M4B to multiple MP3's (divided by chapter)? I've seen a few that go the other way around.

I tried "Free M4a to MP3 Converter", but it didn't separate the chapters.

Thanks