I saw two questions on locating these surfaces ahead of CG:
How are these the same or different control surfaces?
The rudder is mobile, and typically attached to the aft edge of the vertical stabilizer. It provides controllability in yaw (it allows the aircraft, if necessary, to point in a different direction than the one it's moving).
The rudder allows the aircraft to slip sideways when you want it to; the vertical stabilizer keeps it from slipping sideways when you don't want it to.
(Original via flickr.com)
In order to deserve its name, a stabilizer must be located aft of the center of gravity. Once it is shifted ahead, it will become a de-stabilizer.
The only way to laterally stabilize an aircraft with a vertical surface ahead of the center of gravity is to make it moveable and actively controlled, either being slaved to a gyro or, even better, continually adjusted by a computer. In other words, any forward vertical stabilizer is a rudder.