just post it here & submit.
In the discussion area, you click on the thread or question you want to read or look at and you'll see their comment displayed at the top and underneath their comment will be a statement "Post a Comment" and under that is a box with "To" above it and you can fill in the person's username you want to reply to, or you can leave it blank, and under that is a box with "Comment" above it and you type your comment and then hit "Post A Comment" below the box you typed a comment...your comment will show up under their comment.
Take care...