CNET  
   Contains a free demo download and user opinions of the game.
   http://download.cnet.com/downloads/0-10034-108-58918.html

Planet Half-Life: Opposing Force  
   Walkthrough, tips, downloads as well as strategies for both the single player and online multiplayer version.
   http://www.planethalflife.com/opfor/

Justice for all [JFA]  
   Includes screenshots, pictures, profiles, and downloads.
   http://www.geocities.com/stryker_calhoun/

GameGuide.com  
   A complete game guide including first-person shooter basics, weapons descriptions, walk-throughs, cheat codes, and easter eggs.
   http://www.gamespot.com/gamespot/guides/oppose_gg/