Other Magic House Rules

See Spellcasting by the Book (Roleplayer #25).
I use the basic concept presented in the referenced article combined with the table above. Assuming that you don't already know the spell (that's why you are using the Libram!), your base skill level is IQ-5 (MH) or IQ-6 (MVH).

Modifiers
-1 per spell Spell prerequisite not known (at least 1 point and 12+ skill. including all prerequisites for each spell...)
-3 Requisite Advantage not possessed (i.e. Animal Empathy for Beast-Soother)
-5 per level difference Requisite Magery Level not met

An Example
Joe the apprentice has a libram from his Master's library. He wants to cast Telepathy (MVH). He has IQ 14, Magery 1, and he knows Sense Foes, Sense Emotion and Truthsayer.

Time to cast: 4 minutes (base 4secs * 60)

Skill Level: 14 IQ
-6 MVH (IQ-6)
+1 Magery: 1

-1
-1
-0
-0
-0 Prerequisites:
Mind-Sending
Mind-Reading
Thruthsayer
Sense Emotion
Sense Foes
+4 extra time
(64 minutes)
11 :adj. Skill Level

Thaumaturgy

Mental Very Hard

(This option would really increase the power of a mage)
This skill lets you cast a spell from a Libram without the Libram. Make a skill roll for each spell that you don't know. Success let's you proceed as if you had the Libram, failure means you can't. Remembering each spell gets progressively harder, thus you must take a -1 modifier (cumulative) for each roll after the first.
Example: Using the example above, assume Joe's Thaumaturgy skill is 15. He'd have to make a roll at 15 (Mind-Reading), 14 (Mind-Sending), and 13 (Telepathy). If he succeeds on all rolls then he can start casting as above. (Note: if he had failed only the Telepathy roll, he could try casting Mind-Sending instead since he remembered that much).

Spells

College: Music see Music Aspected Magery ...

College: Ley see Ley Lines

References: