Provided that you are using the ABB driver from the ROS-Industrial community, you can find the topics it publishes and subscribes to on the abb_driver page.
Most users will want to interact with the joint_trajectory_action node. It accepts msgs of the type control_msgs/FollowJointTrajectoryActionGoal on the joint_trajectory_action/goal topic (similar to other action servers controlling arm motion).
The joint_trajectory_action node then translates these msgs into suitable trajectory_msgs/JointTrajectory msgs for the /joint_path_command topic, to which the specific driver nodes subscribe. In this case the motion_download_interface from the abb_driver package.
We would like to use a planned path from Moveit (Rviz) to create our trajectory and then send that trajectory to the robot.
The ROS-Industrial drivers all implement the basic (standardised) ROS interface for arm control that lets MoveIt (or one of it's controllers) interact with them. Controlling a ROS-Industrial driver (or the arm connected to it) is no different from working with any other ROS driver implementing the same interface.
There isn't yet a support package or MoveIt configuration package for the IRB140, but they aren't too difficult to create. See wiki.ros.org/abb for some existing packages, the Create a URDF for an Industrial Robot tutorial for some pointers on how to create a proper URDF, and the Create a MoveIt Package for an Industrial Robot tutorial for ROS-Industrial compatible MoveIt configuration packages.
You might also be interested in the ROS-Industrial training exercises. They take you through the process of setting up and interacting with some (simulated) industrial robots, and also planning and execution motions with them.
It would help if you could tells us what 'having difficulties' means exactly. What are you trying to do, and what isn't working? What do you think should happen?
Sorry for the vague question on Friday, it was a long day of learning and research. I added more information to the question up above.