Last Official version: Rules Compendium (p225)
Creatures which are immune to poison damage are not immune to the non-damaging effects of powers with the poison keyword. However, they are immune to all effects of poisons described as items (for example, alchemical substances).
When poison is applied to a weapon or projectile, a creature which is immune to poison damage is immune to all effects conferred by that poison. Effects which are not conferred by the poison (such as the hit/effect line of a power used to deliver the poison) are not affected by the immunity.