Well, if you're just looking at a thread and thinking 'Hey, that looks like fun!', I would say it's best to ask one of the participants directly, like in a PM or something. You may get in, you may not. I asked on a prior occasion about getting into a particular conflict because another person's character in that conflict was relevent to one of MY characters, and that it would be great story if she had been on the other side of it. The guy I was talking to thought it was interesting, but after some discussion with the other player, it was decided to keep it between them. It happens.
