Automatically replacing MP3 ID tags

Does anyone know of a free util that will rewrite ID3 tags automatically? I have a lot of compilation albums that have been tagged with the compilation name in the artist field and then the song and artist name in the song name field eg

Motown Compilation - Smokey Robinson & The Miracles / Shop Around

I'd like something that would run read the tags and put everything before the / in the artist field and everything after / in the song name field. Anyone know if something like this exists? If it could rename the files too it would be a bonus