The Nokia PC Suite software changed a while back from having loads of individual files in the backup to a single huge combined archive. Is your phone compatible with older versions of the software?

I don't think the archive format is that amazingly difficult to decipher. I did reverse engineer some of it but never finished.

It is purposely made to be difficult to transfer ringtones, wallpapers and games. It is so it's harder to pirate your super duper poppy crap ringtone/wallpaper/games.