Another Steam forum thread by user Scuzball explains how to switch over to the undead side and start a game against 4 AI survivors using just a few console commands. Meanwhile, fans anxious to test drive the zombies from the versus mode can get their fix-in the single-player game, anyway.
It requires the use of an Xbox 360 controller connected to the PC, but assuming the player has a controller it's a relatively easy process. User TheBusGuy on the Steam forums has written a 'guide' to playing with two players on one PC. After less than 48 hours, a bit of trickery has yielded split-screen play, playable zombies from the versus mode, and even an old friend of Counter-Strike fans, the classic map de_dust.
Fans have had a field day with exploring what's possible in Valve's Left 4 Dead since the demo for the PC version was unlocked for pre-order customers yesterday.
