Anthousa has a heroic effect that allows it to turn lands into attackers whenever a spell targets it, but Viper's Curse prevents effects from being activated. So, does the heroic ability get activated or not?
Assuming that you are casting Viper's Kiss on your opponent's Anthousa, the heroic ability will not trigger, but this has nothing to do with the effects of Viper's Kiss. Anthousa's ability begins "Whenever you cast a spell that targets Anthousa, Setessan Hero, ..." (emphasis added), where "you" refers only to Anthousa's controller*, which is not the player who is casting Viper's Kiss, and so Anthousa's ability won't trigger.
If, on the other hand, a player casts Viper's Kiss on his/her own Anthousa, heroic will trigger, but whether the Aura stops triggered abilities or not is moot; the triggered ability triggers while the Aura is still on the stack, and thus not affecting Anthousa yet, and so even if Viper's Kiss prevented triggered abilities from triggering (which it doesn't, and which I don't think any Aura does anyway), it would be too early to stop the heroics.
* From the Comprehensive Rules:
109.5. The words "you" and "your" on an object refer to the object's controller, its would-be controller (if a player is attempting to play, cast, or activate it), or its owner (if it has no controller). For a static ability, this is the current controller of the object it's on. For an activated ability, this is the player who activated the ability. For a triggered ability, this is the controller of the object when the ability triggered, unless it's a delayed triggered ability. To determine the controller of a delayed triggered ability, see rules 603.7d-f.