quick links -> edit options -> thread display options -> thread display mode.
that lets you choose chronological, reverse chrono, threaded, or "hybrid."
i like chronological, or "oldest first", and then hit "view first unread" at the top of the thread.
explanations here:
http://www.986forum.com/forums/faq.php?faq=vb_board_usage#faq_vb_threadedmode
good luck!