I think RSS is the ticket for you. If you're not familiar with the concept, there's a link at the bottom of every dpreview.com page, and you can get an overview of how it works here: http://www.whatisrss.com/
You can set up a feed to get new posts for as many or as few forums as you want. (Its what I do to read the daily "news" on this site, very handy.)
For a personal recommendation, if you're on a Mac like me I really like Vienna ( http://www.vienna-rss.org ). But both Safari and Internet Explorer now include embedded RSS news readers, and you can even use Google Reader online ( http://www.google.com/reader ) to accomplish the same thing.
If in fact RSS feeds from these forums only include the original post in a thread, then someone here with more forum experience might be able to explain how to subscribe to a thread for the followup posts.