Here is the definition of Quicken Spell from DnD:
Quicken Spell:
You can cast a spell with a moment's thought
Benefit:
Casiting a quickened spell is a free action. You can perform another action, even casting another spell, in the same round as you cast a quickend spell. You may only cast one quickened spell per round. A spell whose casting time is more tha 1 full round can not be quickened. A quickend spelll uses up a spell slot four levels higher than the spell's actual level.
So here is how it should work in NWN:
When a quick spell is cast, there is no verbal or somatic components. It just happens as though you used an item (this is what happen pre-hotu). After the quick spell is cast you may cast another normal spell. All spells in NWN have a casting time of 1 round. So you may cast 1 quick spell and 1 normal spell in 1 round. If you have haste, casting times are cut in half, so you may cast 2 normal spells per round, like we all know. If you cast a quick spell with haste you may cast 2 more spells that same round since their casting time is 1/2 a round, for a total of 3 spells per round. It obviously doesn't work that way in Hotu.. in fact it really doesn't work at all and is a uselsss feat.