Eternal Silence is a free Source mod and is officially supported by Steam. If you don't have Steam, download and install it first.
With Team Fortress 2 being F2P you now don't need to own any other Source games, just download Eternal Silence through Steam and you're good to go!
Get the Dedicated Server files using the HLDS Update Tool with the game "esmod"
See srcds.com for general information on setting up a Dedicated Server.