In any case, you will endup downloading more then just a single forum, cause every forum has many links to many other pages ...
To avoid downloading other pages, you may be able to specify that browser should download only pages containing "f=254"
Every forum has it's uniq ID number and this forum ID = 254. Every page of this forum contains "f=254" as a part of URL. If a browser you choose allow for filtering URL by substring, you should specify to filter and download only URL containing "f=254", or you may get all pages from this site, over a billion pages ...