What might be interesting is to have a "post vote" system where, upon reading a topic, you can vote for "this topic belongs here" or "this topic belongs in the other forum", if the net vote was over 5 to move it would be moved to the other forum.
I don't know why, but I don't like this idea of voting...
But yeah, having passwords and such and openly being divisive would ruin the forum.
I suggested to have 2 different boards, but where anyone could post anywhere he likes, as long as it corresponds to the topic. The only difference would that one of the boards would be for helping beginners learn.