MP3 id3 Issues between OSes

Two issues, both related: I play my mp3s in iTunes and occasionally windows media player. I have issues where WMP will not have the information that iTunes does and vice versa. Is this information stored with the mp3 file or elsewhere? Also, I recently switched to Vista, but for some reason about 50% of the id3 information is totally gone.

What program or method do you recommend for not losing that info between music players and when reformatting, etc?