All of the tutorials to get this working are kind of a pain and half of them are out of date, so I made a bunch of Steam shortcuts to launch the game in split-screen mode. This assumes you have two xbox 360 controllers, which should be turned on before launching it. This also assumes Steam is installed here: C:\Program Files\Steam\Steam.exehttps://dl.dropbox.com/u/24682992/l4d-splitscreen.zip
Unzip, turn on/plug in your controllers, double-click on the campaign you want.
Of course, links and such tend to die after a while, and you may be (rightfully) leery of downloading and running things from some guy on the internet, so here's how to make your own:
1) Make a copy of the Steam shortcut on your desktop.
2) Go to the properties of the copied shortcut and make the target look like the following:
"C:\Program Files\Steam\Steam.exe" -applaunch 500 -console +ss_splitmode 1 +ss_map l4d_farm01_hilltop
-applaunch 500 means "Run Left 4 Dead".
- console enables the console.
+ss_splitmode 1 is horizontal splitscreen; +ss_splitmode 2 is vertical.
+ss_map l4d_whatever loads the map. Here's the valid map names of the beginning of each campaign in my copy of L4D:
Blood Harvest l4d_farm01_hilltop
Crash Course l4d_garage01_alleys
Dead Air l4d_airport01_greenhouse
Death Toll l4d_smalltown01_caves
No Mercy l4d_hospital01_apartment
I have no idea what this is but maybe I'll try it one day tutorial_standards
I included a readme.txt that explains how to choose your character; not going to bother posting that here because this post is too long already. Enjoy. -m3lang3