Free advice:
Putting up a non-load bearing wall to partition a room is a no-brainer but doesn't really require a carpenter. You need a guy who can toss up some basic framing, drywall it, and paint it. My drywall guy could knock it out pretty fast. I can put you in touch with him if you like.
Taking out a wall is another story all together though.
First you need to determine if the wall is load bearing or not.
If non load bearing:
You need to determine if there are any electrical circuits in the wall. If there are then you need an electrician or someone electrically competent to move and eliminate or reroute the circuits as the wall is removed. Also, you will need a drywall and flooring guy (carpet,tile, laminate) to patch the floor, ceiling, and connecting walls after the wall is removed.
If load bearing:
You need to determine the correct size beam (exposed or not), build temporary walls to support the load. Remove the wall, install the beam, and then after that is done you will need to follow the same procedures previously mentioned for a non load bearing wall.