What is the problem you're trying to solve? Why is one long room more desirable to you than two smaller rooms? Are you still going to have a dining area and living area? Did you consider just expanding the size of the opening between the rooms?

Have you gotten quotes on moving the fireplace? Is it wood or gas burning? In a lot of circumstances moving a fireplace is not a trivial matter. Is the furnace or hot water heater using the chimney for venting?