Hi Russ
When, after having composed your reply, you click on Preview, you should see your posting as it will appear on the forum at the top of the screen. Below this you will see the compose message field. If there is anything you want to change, edit this as usual. You can then either click on Preview again to see the effect of your changes, or click on Post (to the left of the Preview button). Your reply should then appear under the original message. Note that you may need to scroll down the page to see it.
Hope that helps, but do post again if not!
Nick
P.S. Remember that, if you are posting to a thread which already has a lot of messages, you may need to go to page 2 or 3 to see your message. All replies appear at the very bottom of the most recent page.