[3.5] Ways to learn spells from a different class list

[Zeful]

I always thought wizards could learn other spells through RP means, you were just limited when you leveled up and selected spells.

I think there's a spell that allows you extract spells from someone's blood.

Yes that is how the various wizard rules for spell scribing are supposed to work. It should be self-evident due to the wording of that sentence that that's not how it works in practice at all.

And technically, any class can learn any spell, but requires DM approval after you have spent something like 1000 gold and week per spell level.