Just found out that http://dbforums.com/search.php doesn't have any option for searching only the local forums (as against local forums + newsgroups). I'd personally want such an option because most of the times, the queries spanning newsgroups tend to pick in a lot of unrelated posts.
If you want to hide usenet posts from a search, just check the box on the search page.
If you want to search <i>only</i> usenet posts, then you can simply select the appropriate forum from the drop down. All child forums are included in the search, so you can simply select 'Usenet Groups' from the drop down.
If you select a specific forum or category to search, the 'Hide usenet' filter is overridden.