This is a forum for mIRC related issues, i assume you asked simply because its a forum and therefore someone may know how to help you on another one? Which is better than another assumption, which is that you want us to help you hack into a forum. Needless to say, we wouldnt help you even if we could if thats the direction you are aiming in.
Each forum is different, we have no way of knowing who its admins are or how to contact them, and of course we have nothing to do with them. I seriously doubt any forum "software" or admins would make it a simple matter for someone to make themselves a moderator simply because they want to. It isnt surprising that yahoo admins wont help you, as im sure you realize. My only suggestion to you would be to try to contact the person who set the forum up, or any moderators it may have.