How do you play left 4 dead without steam?

If on Xbox 360 go on versus mode play with friends and create your own lobby get a second player choose your campaign and u should be able 2 play.

Here is another way (for PC):

First go to Keyboard/mouse and then enable developers console.

Then open a single player game

type in these codes:

sv_cheats 1

sb_all_bot_team 1

sb_unstick 0

jointeam 3

Then you should be able to play as infected