I use a completely different approach of one table for each forum.
My table looks like this
CREATE TABLE IF NOT EXISTS tblForum
ID BIGINT NOT NULL auto_increment,
Title VARCHAR(100) NOT NULL,
Parent BIGINT NOT NULL DEFAULT 0,
Owner BIGINT NOT NULL,
Message TEXT NOT NULL,
IP VARCHAR(15) NOT NULL,
Posted TIMESTAMP NOT NULL,
LastPost TIMESTAMP NOT NULL,
PRIMARY KEY (ID),
INDEX Title (Title),
INDEX Parent (Parent),
INDEX Owner (Owner),
INDEX Postec (Posted),
INDEX LastPost (LastPost)
this simple table gives me all I need to list the number of posts a use has, give the original creator edit abilities, allow threading of messages and display records in the order they were last posted including replies.