[Rokenn]

The spell book skills control what level spells you can learn. Basicly to learn a spell you have to be high enough level and have the skill level, if you are lacking either you can not learn the spell. Here is a short breakdown (I think the full info is another thread, not sure which one):
1) Minimum Level requirement:
Pure Caster Classes: Mage, Priest, Psionic, Alchemist, Bishop
Hybrid Caster Classes: Monk, Ninja, Ranger, Samurai, Lord, Valkyrie
Spell Level .... Min. Class Level
................. PURE .. HYBRID
1 ................ 1 ....... 5
2 ................ 3 ....... 7
3 ................ 5 ....... 9
4 ................ 8 ...... 12
5 ............... 11 ...... 15
6 ............... 14 ...... 18
7 ............... 18 ...... 22

2) Minimum Skill Requirement
To calculate your effective skill level for a given spell:
* Take your highest spellbook skill (Wizardry, Divinity, Psionics, Alchemy) that the spell in question appears in. Important for bishops or class-changed characters, since many spells appear in multiple books.
* Add 10% of your *natural* skill in that spell's realm. This doesn't include temporary skill bonuses such as those from iems.
Spell Level ..... Min. Effective Skill Level
1 .................. 0
2 .................. 15
3 .................. 30
4 .................. 45
5 .................. 60
6 .................. 75
7 .................. 90

Hope that helps.