If you have never played Modular Combat before, this is the version you want to download. It should install automatically to your "steam/steamapps/sourcemods/" directory. After running it, navigate to that folder and make sure that there is a "modularcombat" folder present and then restart Steam. Modular Combat requires the Orange Box (HL2, HL2:Ep1, HL2:Ep2, HL2DM)
Modular Combat 2.0.5, released November 30, 2010.