In TFT/HOW style rules, casting is dependent on the wizard to the roll dice vs. his IQ to try and successfully cast the spell. If the roll is successful, the results are applied to the target. There is no resistance roll for the target except in the case of illusions and then it is a disbelieve roll by the target.
In the HOW basic rules (p46) there is a basic method given for spell resistance. While simple and easy to execute, in light of the Magi Carta being published, there is opportunity to improve upon the idea of spell resistance in this system.
As discussed on the Heroes & Other Worlds G+ site, below is a (still) simple but a bit more detailed method of spell resistance for HOW:
The target of a successfully cast Timed (T) or Permanent (P) spell may attempt to resist the spell's effect by passing a test of X+1/IQ.
In this equation "X" represents the number of dice the Wizard used originally to successfully cast the spell and then add +1 die to the test.
Example: a Wizard casts a 3/IQ Sleep spell, this would take a 4/IQ test (3+1=4/IQ) to be passed by the target to resist the spell's effect.
If the spell is successfully resisted, the target pays the same EN price the original casting Wizard did when the spell was cast.
Example: The Wizard who successfully cast sleep and spent 2 EN doing so. The target tests 4/IQ and the spell is successfully resisted by the target. The target then must pay 2 EN in having resisted the spell.
If the spell is unsuccessfully resisted, the target pays no EN, and the successfully cast spell effects are applied to the target immediately.
This option does not give back EN spent by the Wizard that successfully cast a spell, but it causes the target of the spell to spend that same amount of EN if the spell is successfully resisted.
So as a net/net the desired spell effect may not come about, but even if a successfully cast spell is resisted, there is still a blood price paid by the target taking damage with EN loss.