www.steampowered.com
A few weeks ago, a client called "Steam" was released. Its basically a program thats used to launch Half Life, and a few of the more popular mods, and will encompass all future valve games. Its a internet application, you MUST have a connection to play it. You can still play CS1.5 over the lan (you will always be able to do that) and im not sure about versions of tfc etc. But if you want to play 1.6, youll all need to be hooked up to the internet. I would also recommed Wolfenstein Enemy Territory for 20 ppl, its a kickass game at 10v10, especially at lans, cause everyone is yelling "Need ammo!" at each other, and its quite fun.