Try setting emitter type to Point and Direction to disc. Then if your velocity random % = 0 you might get some particles close to each other but you shouldn't get any particles passing over each other.
Beyond this you might want to try something like particle flow in 3D studio max to get more control.
3D animator and VFX specialist
...I totally forgot to mention that the particles can't be moving either. they're just supposed to pop up and disappear. Also I meant to say it's the grid emitter that looks to organized. The box emitter is the one I'me using,, if I make the x,y dimensions really big they don't overlap as much.
Sorry about that. Yeesh, I really shouldn't ask questions to a forum at 2AM, being sleepy makes me retarded.
Here's a screen shot of what I was going for,, just to clarify. The +'s on the ceiling and wall are my particles. http://imgur.com/4Jz9o.png