There aren't many maps for HL2, but if you want to have some fun with the game, download GarrysMod, also on steam.
The Moddb website is a great for Half-Life 2 modifications.
no, not unless you make the map your self an then invite friends to your party
The best way to find one is to buy Half Life 2. There should be an unused product code in there. :)
Most gaming websites online will have a Half Life 2 walkthrough guide. Planet Half Life, Game Spot and Visual Walk Through are 3 examples of such websites.
Put the map in the \maps folder and add the map to the mapcycle.txt.
Impossible, Half life 2 is a program that only operates with all of the maps associated with it. What you saw is probably garrysmod, it let's you go to any map that is compatible with Source and will let you build things pose ragdolls etc.
Half-Life, Half-Life: Blueshift, Half-life: Opposing Force, Half-life: High Definition pack (might not classify as a game), Half-Life: Source, Half-Life 2, Half-Life 2: Episode 1, and Half-Life 2: Episode 2. Eight games total not including countless mods created by fans that you can download for free on moddb.com and fileplanet.com. Other games by Valve software include Left 4 Dead, Left 4 Dead 2, Portal, Portal 2, Counter Strike, Counter Strike: Source, Team Fortress, Team Fortress 2, and Alien Swarm. Another Half-Life game would be Half-Life: Decay. You might also be able to count Half-Life Deathmatch and Half-Life 2 Deathmatch.
you start with half life 2, then you play half life 2 episode 1, then you play half life 2 episode 2, so you are basically playing them in the order they are in at the game select screen (where you choose any of the half life games, portal or tf2)
No, only Half-Life and Half-Life: Decay.
Half Life 2 cheats are available through IGN, GameSpot, CheatCC, PlanetHalfLife, GamesRadar, VideoGamer, NeoSeeker, WikiCheats, SuperCheats, and GameRevolution.
Half Life 2 Half Life 2: Episode 1 Half Life 2: Episode 2 Portal Team Fortress Hope this helps ;)
Buy Half Life: Source Or Buy Garrysmod a Half-Life 2 Modification and get the addon "Half-Life Rennaisance" Link to Half Life Rennaisance: http://www.garrysmod.org/downloads/?a=view&id=57033 Enjoy!