Back in 2011 I wrote a post in answer to the questions asked on this forum around copying Autodesk Inventor assemblies.
Since I first wrote that post, it has been read nearly 20,000 times!
I've brushed it off a little, added a link to the new Vault 2015 Design Copy tool and added a flowchart to help you identify which tool to use.
Enjoy!
http://cadso.co/CopyAssembly
Paul