How to get work Half-Life under Xash3D:
step-by-step instruction for anyone.
It is important to understand, that Xash3D is an independent game engine. It's not a mod for Half-Life, so to get work Half-Life under it, you have to make a separate installation of the game. Please follow these steps carefully and you won't confuse with anything.
1. Please install a Half-Life game properly at first. Currently, a full version of Half-Life can be purchased and activated via Steam. If you have a CD with an old WON version of Half-Life, you can use it too. But please remember, that it's recommended to update your WON version of the game with a patch 188.8.131.52 to be prepared for running latest Half-Life mods also, not only Half-Life itself. If you are not sure which version of the WON game you have installed, just launch the game and look at the right lower corner of the game menu screen. There are some numbers with your game version. If it's not a "v46/184.108.40.206", please update your game. But you don't need to update your Steam version of the game with this patch. Any Steam version of the game should be compatible and ready for running latest mods via Xash3D, but be sure to follow this instruction carefully, especially step 6 - some files have to be added/replaced to have all things working properly.
2. Download the latest version of Xash3D Engine. Currently, it's a build 4097 (v0.99). You can get it at the "Files" section. After downloading you will get a Xash3D_build4097_with_extras.zip file on your computer.
3. Now you have to create a separate folder for Xash3D installation. You can create this folder anywhere you want, but please don't create it inside that directory where your Half-Life is installed already (don't be a noob, LOL). It's better to use simple path to this folder and give it an appropriate name, something like "D:\Games\Xash3D". This folder will be your main Xash3D game directory.
4. Locate and open a folder with a basic Half-Life game content. For the WON version of game it can be something like "C:\Sierra\Half-Life\". You will see a "valve" directory inside. For the current Steam version of the game it can be something like "C:\Program Files\Steam\SteamApps\common\Half-Life". You also will be able to find a "valve" directory inside it.
5. Copy the whole "valve" folder with all of its' content from your Half-Life game folder directly into the main Xash3D game directory (which was created at Step 3). So after that you get something like "D:\Games\Xash3D\valve" with a basic game content. If you are using Steam version of the game as a source, after copying (extracting) of "valve" folder also check inside "valve\sound\common" folder. There are some launch_*.wav files. Copy them to the "valve\media" folder (these sounds are required for Xash3D game menu, but they present in this folder only in WON versions of the game).
6. Proceed to extracting a content of the Xash3D_build4097_with_extras.zip archive into the main Xash3D game directory. At first, you will get 2 more archives: Xash3D_build4097.7z and Xash3D_build4097_extras.7z. 7z files are 7-Zip archives, which can be extracted with 7-Zip program or with any other appropriate archiver. Continue their extracting into the Xash3D directory with overwriting of any existing files (some files in the "valve" folder have to be replaced, especially dll-files, otherwise you may get critical error and be unable to play the game). Finally, you will get the Xash3D directory with "docs", "source code" and "valve" folders inside, plus files #hl.exe, hl.exe, Install Notes.txt, menu.dll, readme.txt, vgui.dll and xash.dll.
7. Now you almost ready to run the game. But firstly, create a shortcut for hl.exe (located in the Xash3D directory) and put it onto your desktop (or into the Programs menu, for example). If you want to enable a console in the game, you have to edit a properties of the shortcut (right-click the shortcut and select a "Properties" tab in pop-up menu). Check the "Target" field and add there parameter " -console" (with space, but without quotes) after hl.exe (it should look like "...\hl.exe" -console). Alternatively, you can use " -dev" parameter. Click "OK". There is also #hl.exe in Xash3D directory, which can be used to start a dedicated server for multiplayer game (if you are interested in this feature).
8. Start your game via the created shortcut. At the first launch, engine will try to detect your current desktop resolution, and use it in a fullscreen mode. If it fails in doing so (your desktop resolution is not supported, or else), it will use a windowed mode and 800x600 resolution. When the game menu appears, you be able to edit your game preferences (video mode, resolution, sound effects, controls etc.) via "Configuration" menu. Please note, that in the "Sound" menu there is "Enable sound interpolation" checkbox. It's unchecked by default, because this is an experimental feature in Xash3D. It can cause some wrong sound effects in certain situations. So enable it "on your own risk", if you really want to try. It's recommended to restart the game after significant changes of configuration (video mode or resolution settings, multiple changes of control keys etc.) to apply and save new settings properly. In case of engine's crash applied settings will not be saved.
9. If you want to play any Half-Life or Xash3D mod, you have to install it or extract its' content into a separate folder inside a main Xash3D directory (same as for the standard Half-Life game). Follow an instruction that is appended to a mod, but make sure that any mod (with all of its' content) was placed into an individual folder. Any properly installed mod can be selected and activated via "Custom game" menu. You can also create a custom shortcut to run any mod. Just create a copy of the shortcut for hl.exe and add in the "Target" field parameter " -game FOLDERNAME" (with space, but without quotes) after hl.exe. "FOLDERNAME" here is a name of the folder where your mod is located. For example, to run Opposing Force (when installed) you have to add " -game gearbox" parameter after hl.exe (it should look like "...\hl.exe" -game gearbox). In fact, it's all the same system, which you can use to run any mod under standard Half-Life. Please note, that "FOLDERNAME" should not contain spaces (legit names are like "foldername" or "Folder_Name" or "Folder-name" or "FOLDER.NAME", but not like "Folder Name").
10. Make sure you have read an additional information about Xash3D posibilities and features (which is containing in documents in the "docs" folder, plus in those text files in the main Xash3D directory). Some information is also avaliable here, at ModDB. Please read the details, before you ask about something, that you don't know yet.
P. S. If you've used command line parameter for enabling the console, but it still doesn't work, check "gameinfo.txt" in your current mod's folder for the line secure "1", delete this line and save changes.
P. P. S. Be sure to check this article and users' comments below it for the information about supported mods and recommended conditions / advices to play them.