This week, on Thursday (04/22/2010), was released DLC The Passing of the project for Left 4 Dead 2. It includes:
A new single player and co operative company in which the four survivors of L4D2 meet the characters of the first game;
New multiplayer game modes, are called Mutations; is a diverse set of mods, very raznoobrazyaschih gameplay, all scheduled appearance in 1920 of mutations from Realism Versus Mode before Chainsaw Massacre, giving players the chainsaw with an unlimited supply of fuel;
A new weapon: golf clubs, and M 60;
A new class of zombie boss (the fallen vyzhivshye);
New version of AI Director 2.0, which allows the director to modify, at its discretion, weather effects, move objects, changing the
Minim System Requirements:

Operating System : Microsoft Windows XP / Windows Vista (32 & 64 Bit) / Windows 7
Processor : Intel Pentium IV at 2.0 Ghz or equivalent AMD
Video Card : 128 MB VRAM DirectX 9.0 compatible with Shader Model 2.0 support.(nVidia GeForce 6600 / ATI Radeon X800)
Memory : 1 GB (XP) / 2 GB (Vista)
Hard Disk : 7.5 GB of free Hard Drive space
Sound : DirectX 9.0c compatible sound card
Direct X : 9.0c
Controls : Keyboard & Mouse / Windows compatible controller
Installation : DVD ROM Drive / Digital Download

Recommended System Requirements :

Operating System : Microsoft Windows XP / Windows Vista (32 & 64 Bit) / Windows 7
Processor : Intel Core 2 Duo at 2.4 Ghz or equivalent AMD
Video Card : 256 MB VRAM DirectX 9.0 compatible with Shader Model 3.0 support.(nVidia GeForce 7600 / ATI Radeon X1600)
Memory : 1 GB (XP) / 2 GB (Vista)
Hard Disk : 7.5 GB of free Hard Drive space
Sound : DirectX 9.0c compatible sound card
Direct X : 9.0c
Controls : Keyboard & Mouse / Windows compatible controller
Installation : DVD ROM Drive / Digital Download

Extras. installation information:

This addon. Unpack in the folder containing the L4D2. If the game does not start, necessarily (!) To clean the folder addons (/ left4dead2/addons), in particular Sourcemod (version 1.3.1 does not work either) wait for the new version. Vpk addons game takes normally, they can leave.
Set necessarily 2.0.1.1 patch!
Set 2.0.1.3 already installed 2.0.1.2 similarly to unpack in a directory with the game