You likely are, you need the assemblies that are included with the SDK that comes with SQL server. Be sure you installed the SDK when you installed SQL server.
(screenshot taken from a random google image search, the highlighted item is what you need)
By default they are located at a path similar to C:\Program Files (x86)\Microsoft SQL Server\100\SDK\Assemblies
The version number may be different for the version of SQL server you have installed.