I think it's too much. But then, I've never been a fan of props, period.
Originally Posted by Cryotech
That, I think, is too much by anybody's standards. The occasional lighting change or soundtrack can be helpful (that's about as far as I've gone with this stuff; Spiderbait's "Ghost Riders in the Sky" makes a great battle track for Deadlands), but unless your players know that this is what's going to be happening, and have agreed that it sounds good beforehand, I wouldn't do it.
And by props, I mean setting the mood through ambient lighting, sounds and even changing the location of where we play according to where the players are in the game. For example, if the PC's are all in a house, the session could be held in the dimly lit kitchen, and if they're hiding in or fortifying an old barn, the next one could be held in an old barn, the next outside..near a campfire or in a tent with a camping lantern lol.
I was even thinking about making lifesize cardboard zombie cut outs and place them in strategic places and have the characters "discover" them through live action RP clue finding / scavenging etc.
As for making a horror game "psychologically believable", well, that's not too hard. First off, realize that you probably aren't going to actually frighten your players. You might get an "ooh, this is creepy" if you do it really, really well, but what with the Mountain Dew and Cheetos being handed around, there's probably going to be a minimum of screaming.
What you're trying to do is get your players to recognize that their characters are scared, and act that out. That's actually not very hard to do. There are a lot of different tools that you can use. The most potent of them is that perennial friend of the Game Master: description. Describe your environments, being sure to mention the way that the shadows seem to stir at the corners of their vision, the slight noises that have no apparent source, and so on. When the monsters show up, don't say "you see a zombie", say "a shambling thing emerges from the twilight, moaning eerily as it shuffles forward. It was obviously human once, but now its eyes are glassy with death, it walks with a twisted, limping gait, and it stinks of grave rot".
Another tool you can use is isolation. Make it clear that the characters are entirely without backup. No one is coming to help. Or maybe someone is coming to help, but they aren't going to get there in time (or, for a twist, maybe they don't want help, as any rescue attempt would spread the infection). Ammo and resources are dwindling fast, and there's nowhere to hide.
Keep in mind, though, that the horror is just a tool to create fun. You don't have to have the entire game be nothing but a bleak retreat from unbeatable enemies. Sometimes the most fun part of a horror game is when the players find the ammo cache and get to mow down their attackers with a minigun.
"I think that I think. Therefore... I think that I am!"
- Jack Snipe, in Erfworld