We install the Haley on an arch window using our posts and knobs. We have two styles of posts. Our original style can be seen in this video http://www.patemeadows.com/Curtain-Hardware_c_41.html. The new version which is much easier to install can be viewed here http://www.patemeadows.com/Finial-AdapterPost-Extender-375-Projection--NEW-IMPROVED-STYLE_p_278.html.
If you are installing the valance straight instead of in an arch shape we use a currtain rod with rings.