The Book of Exalted deeds states
This section begins with a list of sanctified spells, which are available to any class that prepares spells rather than casting them spontaneously. Book of Exalted Deeds, p. 84
What does that mean for a wizard? Does he have to write the sanctified spell in his spellbook? Does he need a teacher or a copy to learn it? Or can he prepare sanctified spells instead of spells written in his spellbook?