Jfood stumbled on this about 2 weeks ago and someone else just posted this process as well on another thread.
If you are wondering which previous post a poster is responding to you click on the name next to the "re:" in the upper right of the post and it will highlight which post above is the reply to. For example jfood replies to a post by "foodie987" yet there are four posts by foodie987 already in the thread. In the upper right of jfood's reply it will read "re: foodie987". If you click on it, the replied to post will turn yellow above.
Jfood apologizes for the horrible grammar but it is extremely helpful.