There are many people, like myself, who are upset that the previous owners have painted all the once beautiful molding. I am wondering why you are interested in painting dark wood? If it's the maintenance, you will have more difficulty keeping mainted molding "clean" looking than if you simply refinished the molding. It is only a matter of using a finish remover on the wood and then re-shellacing or urethaning the wood again. Is this an older home? If so, you may find the warmth and character of the room lost if you simply paint over it.
I am struggling through stripping over 60 years of paint off of my moldings right now.