Prove U're the best.

How to install 1v1 on local server (Windows Users) :

STEP 1 :
Download Sourcemod (SM), Metamod (MM) and Confogl (CO) :

http://www.sourcemod.net/smdrop/1.3/sourcemod-1.3.7-hg3069-windows.zip
http://www.metamodsource.net/mmsdrop/1.8/mmsource-1.8.5-hg749-windows.zip
http://confogl.googlecode.com/files/Confogl-2.2.2-RC.zip

Download Metamod.vdf :
http://www.sourcemm.net/vdf

Unzip the files.

STEP 2 :

Copy SM, MM, and CO in Steam/steamapps/common/left 4 dead 2/left4dead2/
Copy Metamod.vdf in Steam/steamapps/common/left 4 dead 2/left4dead2/addons

STEP 3 :

Edit admin_simple.ini (with Notepad),
wich can be found at Steam/steamapps/common/left 4 dead 2/left4dead2/addons/sourcemod/configs

Simply add a line with this form :
"YOUR_STEAM_ID" "z"

Save,

You're Good to go.

Warning : You may have some problems connecting to servers online.
If so, move the content of Steam/steamapps/common/left 4 dead 2/left4dead2/addons somewhere else and move it back when you need local.

Special Thanks to Poggus for his Advices.

GLHF.