Demo

Demo is now officially out for those who pre ordered the game
According to an interview with Gabe Newell, managing director and co-founder of Valve, there will be a playable demo of Left 4 Dead on Nov. 6 for those who pre-ordered and Nov. 11 for those who did not, which is momentarily set for world release on steam on Nov. 18, 2008 and in retail locations Nov. 19, 2008 (U.S) and Nov. 21 2008 (UK)

The demo will contain both online and single-player mode, taking place in the movie, "No Mercy", in two chapters, Apartment and Subway. The demo will only feature the survivor co-op side (no playing as boss infected as it's for versus only). It is confirmed that the demo will come out for Xbox360 as well as for PC.

Joining the Infected Team in the DEMO
Otherwise known as "Versus Mode"

-Quick run-through of the demo 

The demo has a 2 maps, and the ability to play Those 2 maps either single player, or co-op. But the ability to play those 2 maps in the "Versus" game mode, has been blocked in the demo...Right?

Wrong

The versus mode allows a total of eight players in the actual release, and allows 4 players to play on the Infected team(as the boss zombies) and attempt to wipe out the survivors team (Contrary to the campaign mode where you can only play as survivors on a team of 4 MAX). The game mode is a little bit buggy, but can be stable if done right.

Right now you're probably asking, How do I take on such a wonderful task of annihilating the survivors? Simple, first enable your developers console by going to Options<Advanced<Enable developers console and then press the Tilde key (` ~) under your escape key, and type in sv_cheats 1.

(Remember, this HAS to be Either Your server, or one that has sv_cheats set to 1 to do this!)

then type the following in your console as well:

ent_fire !self setteam 3 (^-This sets you to the infected side-^) (^-Once you type this in, the game will restart with you on the infected team-^) director_force_versus_start 1 (^-This sets the survivors to start without you - Use only if there are no other players on the survivor team!-^) z_spawn tank

or

z_spawn hunter

or

z_spawn boomer

or

z_spawn smoker (^-these are the things you can spawn as, type one in while dead to spawn as one-^)