fallout_3_alien.zip

This download looks like an addon. You need to extract the downloaded zip and put the addon folder in your Garry's Mod addons folder. You should end up with a directory structure similar to below:

• steamapps
  • common
    • garrysmod
      • garrysmod
        • addons
          • Fallout 3 Alien <-- Addon folder!
            • e.g.
            • lua
            • maps
            • materials
            • models
            • etc

• Fallout 3 Alien/
  • materials/
    • models/
      • player/
        • slow/
          • fallout_3/
            • alien/
              • slow_alien.vmt
              • slow_alien.vtf
              • slow_alien_boots.vmt
              • slow_alien_bump.vtf
              • slow_alien_eyes.vmt
              • slow_alien_glass.vmt
              • slow_alien_glass_fix.vmt
              • slow_alien_glass_hs.vmt
              • slow_alien_glass_hs_fix.vmt
              • slow_alien_hose.vmt
              • slow_alien_hs.vtf
              • slow_alien_metal.vmt
              • slow_alien_skin.vmt
              • slow_alien_technique.vmt
  • models/
    • player/
      • slow/
        • fallout_3/
          • alien/
            • slow.dx80.vtx
            • slow.dx90.vtx
            • slow.mdl
            • slow.phy
            • slow.sw.vtx
            • slow.vvd
            • slow_hs.dx80.vtx
            • slow_hs.dx90.vtx
            • slow_hs.mdl
            • slow_hs.phy
            • slow_hs.sw.vtx
            • slow_hs.vvd
  • Readme.txt

Ziddan, Night Hero22, gokupowergtyt, andresdeleonpaniagua1997, faizamfomegnam, UncleJimmema, Wolf, DECOY panda1, DECOY panda1, Anubis, Texugo Sensual, Poner, Vrbey, Emotional Glowstick, jeffthekiller96, jeffthekiller96, strider, Danny, UncleSHREDDER, Alexander22512, Vinrax, SharkFin, leocardu, Warpath-the-drone swe, Warpath-the-drone swe, Jackie Saint, Wolfman19682005, Wolfman19682005, DukeClowning, SketchyBehavior, A Deep Commitment To Konata, Galle, TomeKK 2Shae[HUN], Baty