Sierra: Half-Life: Opposing Force:Official site includes game overview, news, media, support, forum, demo download, and online ordering.CNET: Contains a free demo download and user opinions of the game.GameGuide.com: A complete game guide including first-person shooter basics, weapons descriptions, walk-throughs, cheat codes, and easter eggs.Justice for all [JFA]: Includes screenshots, pictures, profiles, and downloads.Planet Half-Life: Opposing Force: Walkthrough, tips, downloads as well as strategies for both the single player and online multiplayer version.