Left 4 Dead (L4D) is a new action title from Valve, creators of the Counter-Strike and Half-Life games, and promises to redefine the co-operative genre as those titles did for multiplayer and single player action games.

Set in a modern day survival-horror universe, the co-operative gameplay of L4D casts four "Survivors" in an epic struggle against hordes of swarming zombies and terrifying "Boss Infected" mutants.

Valve’s next generation AI technology, allows for games of 1 to 8 players. Players can play as a Survivor or as one of four types of "Boss Infected," each of whom possess a unique mutant ability such as a 50-foot tongue lasso or a giant belly full of explosive methane gas.

The gameplay takes place across four massive campaigns. The "zombie" population of each mission is choreographed by an "AI Director" that monitors the human players’ actions and creates a unique and dramatic experience for them on the fly.

Set in the immediate aftermath of the highly-anticipated zombie apocalypse, Left 4 Dead features single player, multiplayer and co-operative gameplay modes. Next-generation artificial intelligence tailors the pacing and difficulty ensuring a different experience every time the game is played.

The contest challenges gamers to take a creative photograph of themselves in front of one of the outdoor media placements in London, New York, Boston, Chicago, Los Angeles, Seattle and the San Francisco Bay Area.

Contest rules and submission guidelines can be found here. All entries will be reviewed and judged by Gabe Newell, president and founder of Valve. The top 25 entrants will win a free copy of Left 4 Dead, and the overall winner will receive a new gaming PC from AMD.

"Working with Gibson Media to infect buses, train stations, highways and city streets in many major metropolitan areas in the US and UK has been a tremendous contribution to the game's pre-launch momentum," said Doug Lombardi, vice president of marketing at Valve. "Pre-orders are now running 95% over those of The Orange Box, and we're getting set to launch the pre-release demo and television campaign to further fuel this momentum."

Early access to the demo begins Thursday, November 6 on both the Xbox 360 and the PC. This pre-order promotion applies to all Steam PC pre-orders and all Xbox 360 and PC pre-orders from participating retailers in North America. The demo will feature single player and co-operative modes, supporting 1 to 4 player games.

On November 11 the demo will be made available to all Xbox 360 and PC and gamers, with no obligation to purchase. The demo concludes on November 18, when Left 4 Dead will be made available at retail outlets across North America and worldwide via Steam.

Left 4 Dead Achievements :

1. Helping Hand: Revive 50 incapacitated Survivors. 20
2. Field Medic: Heal 25 Survivors with a first aid kit. 20
3. Pharm-assist: Give pain pills to 10 Survivors. 20
4. My Bodyguard: Protect any Survivor from an attacking Infected 50 times. 15
5. Dead Stop: Punch a Hunter as he is pouncing. 10
6. Cr0wnd: Kill a Witch with a single headshot. 30
7. Untouchables: No Survivors take damage after contacting the rescue vehicle. 30
8. Drag and Drop: Rescue a Survivor from a Smoker's tongue before he takes damage. 20
9. Blind Luck: You or another Survivor take no damage after being vomited on by a Boomer. 20
10. Akimbo Assassin: Survive an entire campaign using only pistols. 30
11. Hero Closet: Rescue a Survivor trapped in a closet. 10
12. Hunter Punter: Shove a Hunter off of a pinned and helpless Survivor. 10
13. Tongue Twister: Free yourself from a Smoker who has grabbed you with his tongue. 20
14. No Smoking Section: Kill 10 Smokers as they are pulling helpless Survivors. 15
15. 101 Cremations: Set 101 Infected on fire. 20
16. Do Not Disturb: Sneak past all Witches in a campaign without disturbing one. 20
17. Man vs Tank: Single-handedly kill a Tank. 30
18. Tankbusters: Kill a Tank without it dealing any damage to a Survivor. 20
19. Safety First: Play an entire campaign with no Survivors taking friendly fire damage. 30
20. No-one Left Behind: Beat a campaign with all 4 Survivors. 20
21. Unbreakable: Finish a campaign without ever being healed. 30
22. Witch Hunter: Kill a Witch without any Survivor taking damage from her. 20
23. Red Mist: Kill 1000 Infected with a mounted machine gun. 20
24. Pyrotechnician: Blow up 20 Infected in a single explosion. 20
25. Zombie Genocidest: Kill 53,595 Infected. 20
26. Dead Giveaway: Heal a fellow Survivor when your own health is below 10. 10
27. Stand Tall: Survive a campaign without being incapacitated. 20
28. Zombicidal Maniac: Survive any campaign on Expert. 30
29. What Are You Trying to Prove?: Survive all campaigns on Expert. 35
30. Nothing Special: Survive a campaign with no Survivors taking damage from Special Infected. 30
31. Burn the Witch: Light a Witch with a Molotov. 10
32. Towering Inferno: Light a Tank with a Molotov. 10
33. Spinal Tap: Kill an Infected with a single blow from behind. 10
34. Stomach Upset: All Survivors complete a campaign without being vomited on. 20
35. Brain Salad: Make 100 headshot kills. 15
36. Jump Shot: Headshot a Hunter while he's leaping. 20
37. Mercy Killer: Survive the No Mercy campaign. 15
38. Back 2 Help: Leave a safe room to save an incapped teammate and bring them back safely. 20
39. Toll Collector: Survive the Death Toll campaign. 15
40. Dead Baron: Survive the Dead Air campaign. 15
41. Grim Reaper: Survive the Blood Harvest campaign. 15
42. Ground Cover: Save another Survivor from a Special Infected while on the ground. 30
43. Clean Kill: Shove a Boomer and then kill him without him splashing on anyone. 10
44. Big Drag: Drag a Survivor 100 feet with your tongue. 20
45. Chain Smoker: Constrict two Survivors in one life as a Smoker. 20
46. Barf Bagged: Cover four Survivors with Boomer bile at once. 20
47. Double Jump: Pounce two different Survivors in one life as a Hunter. 20
48. All 4 Dead: Kill all four Survivors in one life while playing as a Tank. 30
49. Dead Wreckening: Dole out 5000 total Survivor damage as a Special Infected. 20
50. Lamb 2 Slaughter: As an Infected, incap a Survivor who has entered and left a safe room. 20

System Requirements:

• OS: Windows Vista, XP or 2000
• CPU: 3.0 GHz P4, Dual Core 2.0 or AMD64X2 (or higher)
• RAM: 1 GB for XP / 2GB for Vista
• Disc drive: DVD-ROM Drive
• Hard drive: At least 7.5 GB of free space
• Video: Direct X 9 compatible video card (Video card must be 256 MB or more and should be a DirectX 9-compatible with support for pixel shader 2.0)
• Sound: Direct X9.0c compatible sound card

Left 4 Dead is due for release on PC/Xbox 360 on Nov. 18 in North America and Nov. 21 in Europe. The worldwide Steam release will happen November 18.