I agree with all the above comments. Making it clear from the outset what will and won't be tolerated is a good start, and then enforcing that politely and firmly. Gamers are a mixed bunch, and free-for-all groups can get ugly quickly.

And as a matter of taste, personally I find myself avoiding forums that use dark backgrounds with light text. Aside from being hard on the eyes, I think a more professional dark on pale helps keep the space professional and mature.

As a point of reference, TOG is the best I've seen. I'm a member, but don't use the site much (maybe they're a little TOO big for me to feel comfortable, I don't know). But they do well keeping things civil and organised, from what I've seen.

Will you post a link when it's up and running? I think I'd like to check it out.