Will two NPcs attack each other out of the blue if their alignments are greatly opposite or at teh very least if both are fairly evil? The real question: If I were to plant alignment lowering items on NPCS, say like someone on the street (like a roving guard), is there a chance that they might randomly attack another pedestrian on account of evil alignment?
I don't think alignment alone can make an NPC attack you - the reaction is the key factor there. If it wasn't you'd have to kill every one of the Dark Elves in Arcanum if you were a good char, since they are all evil aligned. I think that to make NPC attack each other, you'll have to work with factions - not sure yet how they work, but I believe you have to work with Code: oemes\faction.mes rules\gamerep.mes files.
Getting an NPC to attack you on sight is more a matter of a combination of the NPC's reaction to a combination of your Beauty, Race (difference being the factor) and Alignment combined. So if you were to plant items on a Half-Ogre that made him uglier and lowered his Alignment, you might be able to get him attacked on sight by other races, especially Dwarfs. Unfortunately, I'm not entirely sure that NPCs react to other NPCs exactly the same way that they react to PCs, so it might not work.
Make a dwarf mage, do every evil thing you can and then join the Dark Elves. Now, without both the jewel of Hebe and a small smoking jacket, even people in Tsen Ang will attack you.
Richard, you missed the point. He was asking about getting two NPCs to attack each other, not NPCs attacking a player character.