You can now get participate in the new Source SDK Update
public Beta, modders can now create single player and multi-player mods based in the
HL2:Episode Two source code. Also it adds the ability that allows users to add custom scenes to Orange Box games.
To run this beta version you will need to add
-beta srcsdk0122 to your command line when you start Steam. This can be done by opening up the Windows shortcut you use to launch Steam and adding
-beta srcsdk0122 right after Steam.exe. For more info
click here.