Would it be possible to delegate searching out to google, just save the user the trouble of typing the extra "site:arclanguage.org"? I know I've seen sites before that used google search for the site's internal search. (Although admittedly, I have no idea how difficult that would be to set up.)
A form that redirects to google should be easy to implement. Another simple approach, that you can do for yourself, is to add a quick search in Firefox. I have this bound to keyword 'a';
The problem with using google to search forums, however, is that it doesn't know anything about threads. When I type 'a module' in FF's location bar, I get 121 hits (should be 122 after I post this ;), and I have no idea how many threads that is - not very practical.