I got my bishop to level 5 last night, but I don't see fireball (or Web) as a choice for me to pick. Is there some other requirement that I am not aware of?

even though your bishop is level 5, his wizardry or fire realm skill might not be high enough yet either. Check here for a list of requirements and all sorts of other goodies on spells and such.
http://www.geocities.com/jandrall/

Thank you, that helped a lot. I visit that page often to look at strategies for leveling my characters, but didn't see the article regarding this topic.