We just published 3 packages for simulating the Darwin OP robot on Gazebo (or to use with the real robot but with some extra work):
 - https://github.com/HumaRobotics/darwin_gazebo
 - https://github.com/HumaRobotics/darwin_description
 - https://github.com/HumaRobotics/darwin_control

We also provide a user-friendly Python API with walking capabilities.

A quick tutorial and demo can be found here:
http://www.generationrobots.com/en/content/83-carry-out-simulations-and-make-your-darwin-op-walk-with-gazebo-and-ros

Credits also go to Taegoo Kim and Bharadwaj Ramesh for the meshes and original URDF on which this work was based.

Enjoy!

Philippe Capdepuy