I am trying to make a "survival" map where players spawn in a building and are bombarded with endless waves of combine. The only problem is, I dont wanna have to deal with idiots killing the other players since this is a pseudo-coop map. So I was wondering if theres a way that I can make players invincible to each other but still take damage from npcs. Kinda like the way the resistance soldiers are in HL2 single player. The only catch is, I can't mod....

arg

If that is the case, is there anyway I could tweak the map to allow for internet play through HL2, I know theres a way to connect to other peoples comps through the console, but it never works, I always assumed it was just because single player maps didnt have spawn points for the second player.....