As a drainage professional I always prefer to install the french drains on the outside of the structure. There are many reasons for this -- see http//www.drainpro for a discussion of drainage to intercept water intrusion. Since yours is a finished basement if you cannot transport the water to an outlet by gravity I would strongly recommend a backup system in addition to the primary drainage system. As to who does this kind of work it will depend on where you live. Ask at your local building supply, landscape supply, builders exchange, and building inspection department.