After the original message, all posts and replies are shown in reverse order, with the most recent post at the top. i.e. your latest post will always appear under the original message, at the top of the first page.
To display oldest posts first, click the 'Flip Order - Oldest First' link below.
To create a site map is simple, see this thread. If you're site is an Instant site them I'm afraid there's no support for site maps yet. Otherwise simply upload the XML site map to your web space and tell Google how to find it via Webmaster Tools.
