> -> I am looking to download a very large message
> board thread (830 pages!), as opposed to the entire
> website, and have hit a snag.

You have to be very careful with downloading "sections" of forums--due to
their nature you will generally, by default, mirror the entire forum.

I would advise you to:

1. Set the start URL as the first page of the thread you want

2. Analyse the URL structure of the forum to produce a list of rules that will
allow HTTrack to only download exactly what you need

3. Define your filters (scan rules), for example:

-* +*.jpg +*.gif +*.png +*.css +*.js
+example.com/forum/attachment.php*
+example.com/forum/view.php?*threadID=12345*

The above rules would disallow everything except URLs that match those
specific files/rules.