Article: Latest Update: Brabham Development Preview (WIP) and Physics Development Blo You can view the page at http://isiforums.net/f/content.php/177-Latest-Update-Brabham-Development-Preview-%28WIP%29-and-Physics-Development-Blog%21
Log in to Steam in your browser, Then follow this link: https://steamcommunity.com/sharedfiles/filedetails/?id=679417795 Click "Subscribe"
So you are registered on steam, and you have installed the steam version of rf2, correct? All you should need to do is click "subscribe" on the link given by Christopher.