Any minecraft 1.6.4 mods that fit a zombie apocalypse theme?

I don't know of any singleplayer mods, but (even though this is a far stretch) you could host a private bukkit server and install the plugin called Apocalyptic (http://dev.bukkit.org/bukkit-plugins/apocalyptic/). I've tried it (and it is pretty fun), but you'd need to know how to set up a server, which a quick search would come up with a ton of results.