A quick and dirty solution is to simply add a column, e.g. U_Notes, to the w3t_Users table, and modify it or view it with phpMyAdmin. This doesn't involve hacking any scripts, and won't incur any maintenance when upgrading to new threads versions.
I would probably use a variation on this, a new table w3t_AdminUserNotes:
CREATE TABLE w3t_AdminUserNotes ( <br /> userid INT(9) NOT NULL, /* user number of user to whom note pertains */ <br /> ownerid INT(9) NOT NULL, /* user number of user who added this note */ <br /> added TIMESTAMP NOT NULL, /* timestamp when note was added */ <br /> note TEXT NOT NULL /* the note */ <br />)
I think having a separate table would be more efficient, since only a fraction of the users would probably have notes.