You locate your original post, open it, and then 'reply' to it, using the
Reply function of your newsreader. For example, in Outlook Express, go to
Message | Reply to Group. An easy way to keep your original post front and
center where you can find it, is to mark it as unread and then 'watch' it.
Easy instructions for these tasks are in the Help file of Outlook Express
and, I imagine, the Help files of any other standalone newsreader software.
Mike Mulligan