Left 4 dead is zombie apocalypse mission you play as Bill for more information visit gtaforums

You also need this mod:
-Bill mod:http://www.gtagaming.com/downloads/gta-san-andreas/player-mods/7561
-Sandking army:http://candykond-sergio.blogspot.com/2011/06/cod-black-ops-russian-armor-truck.html