Well, I've never done a three-people one, but the basic idea is, I send you a PM with part of my post, and then you reply with part of yours, and then if we're including Deep Impact, I'll send it to him and have him reply, then I reply again, then back to you, etc, etc. It's a great way to move along a scene that is filled with a lot of dialogue, instead of taking a whole week of talking back and for, and waiting for another person to reply. Not to mention its all in one, large post, rather than 50 small ones. xD