This is quoted from POR2 manual, so i don't know how accurate will be in NWN:
Monks are proficient with all simple weapons and with all types of armour. In addition, Monks are allowed to add their Wisdom modifier and a bonus based on the level of their AC when not wearing any armour. When wearing armour, a Monk loses his AC bonus from wisdom, AC bonus for class and level, favourable multiple unarmed attacks per round and heightened movement.
Also Monk have several other special skills that are not affected by armour.
"When I am working on a problem I never think about beauty. I only think about how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong."