Insert an Xbox 360 controller. Use a text editor to edit the "360controller.cfg" file in the "\left4dead\cfg folder" directory. Replace its content with the following:

unbindall // Prevent mouse/keyboard control when gamepad is in use (to prevent autoaim exploit)

joystick 1
joy_advanced "1" // use advanced joystick options (allows for multiple axes)

joy_name "L4D Xbox360 Joystick Configuration"
joy_advaxisx 3 // x-axis controls GAME_AXIS_SIDE (strafing left and right)
joy_advaxisy 1 // y-axis controls GAME_AXIS_FORWARD (move forward and back)
joy_advaxisz 0 // z-axis is treated like a button
joy_advaxisr 2 // r-axis controls GAME_AXIS_PITCH (look up and down)
joy_advaxisu 4 // u-axis controls GAME_AXIS_YAW (look left and right)
joy_advaxisv 0 // v-axis is unused
joy_forwardsensitivity -1.0 // movement sensitivity
joy_sidesensitivity 1.0
joy_forwardthreshold 0.1 // movement dead zone settings
joy_sidethreshold 0.1
joy_pitchsensitivity 1.0 // look sensitivity
joy_yawsensitivity -1.5
joy_pitchthreshold 0.1 // look dead zone settings
joy_yawthreshold 0.0

joy_variable_frametime 1
joy_autoaimdampenrange 0.85
joy_autoaimdampen 0.5
joy_lowend 0.65
joy_lowmap 0.15
joy_accelscale 3.0
joy_accelmax 4.0
joy_response_move 5
joy_response_look 1
joy_autoaimdampen 0.3
joy_autoaimdampenrange 0.85
joyadvancedupdate // advanced joystick update allows for analog control of move and look

// Alternate control 1
bind "0" "slot10"
bind "1" "slot1"

bind "2" "slot2"
bind "3" "slot3"
bind "4" "slot4"
bind "5" "slot5"

bind "6" "slot6"
bind "7" "slot7"
bind "8" "slot8"
bind "9" "slot9"

bind "a" "+moveleft"
bind "c" "+voicerecord"
bind "d" "+moveright"
bind "e" "+use"

bind "f" "Impulse 100"
bind "h" "motd"
bind "m" "chooseteam"
bind "q" "lastinv"

bind "r" "+reload"
bind "s" "+back"
bind "t" "Impulse 201"
bind "u" "messagemode2"

bind "w" "+forward"
bind "x" "+mouse_menu QA"
bind "y" "messagemode"
bind "z" "+mouse_menu Orders"

bind "`" "toggleconsole"
bind "SPACE" "+jump"
bind "TAB" "+showscores"
bind "ESCAPE" "cancelselect"

bind "SHIFT" "+speed"
bind "CTRL" "+duck"
bind "F1" "Vote Yes"
bind "F2" "Vote No"

bind "F5" "jpeg"
bind "MOUSE1" "+attack"
bind "MOUSE2" "+attack2"
bind "MOUSE3" "+zoom"

bind "MWHEELUP" "Invprev"
bind "MWHEELDOWN" "Invnext"

// controller2 bindings
cmd2 +jlook // enable joystick look
cmd2 bind "A_BUTTON" "+jump;+menuAccept" // (A) button - Jump -menuAccpt allows us to make selections on hud menus
cmd2 bind "B_BUTTON" "+reload" // (B) button - Reload
cmd2 bind "X_BUTTON" "+use" // (X) Use
cmd2 bind "Y_BUTTON" "lastinv" // (Y) button - swap pistol/rifle or z_abort -used to respawn as a ghost.
cmd2 bind "R_TRIGGER" "+attack" // RT - Main weapon - Primary trigger
cmd2 bind "L_TRIGGER" "+attack2" // LT - Melee
cmd2 bind "R_SHOULDER" "+lookspin" // RB - Fast 180 spin
cmd2 bind "L_SHOULDER" "toggle_duck" // LB - Duck - is also used to give objects to people.
cmd2 bind "STICK1" "vocalize smartlook" // LS - vocalize
cmd2 bind "STICK2" "+zoom" // RS click - Rifle Zoom

// Fixed bindings, do not change these across joystick presets
cmd2 bind "BACK" "togglescores" // (back) button - scores
cmd2 bind "START" "pause" // (start) button - pause
cmd2 bind "S1_UP" "+menuUp" // Hud menu Up
cmd2 bind "S1_DOWN" "+menuDown" // Hud menu Down
cmd2 bind "UP" "Impulse 100" // DPad Up - Toggle flashlight
cmd2 bind "LEFT" "slot3" // DPad Left - grenade
cmd2 bind "RIGHT" "slot4" // DPad Right - health
cmd2 bind "DOWN" "slot5" // DPad Down - Pills

At the main menu, select "Options", then choose the "Keyboard/Mouse" selection. Enable the "Allow Developers Console" option. While playing the game, press ~ to display the console window. Type "Exec 360controller.cfg" and press [Enter], then set your split screen mode with the following console codes: "ss_splitmode 1" ("Horizontal-Cut" for standard monitors) or "ss_splitmode 2" ("Vertical-Cut" for widescreen monitors). Connect to a server. Join the server with the "connect [IP address] 2" console code. You must now set the Xbox 360 controller to player two (with the light on the Xbox logo pointing to "2"). To do this, quickly unplug and reinsert the Xbox 360 controller while the game is running. You can now play in Co-op mode in split-screen.