The problem with doing an integrated search at this point is that because the forum uses flat files to store data, there's really no simple, concise way in which to search data. Can it be implemented? Yes, of course. But that isn't to say it'd be easy, nor that it would perform (and scale) well. Just use Google's search as mentioned by eds.
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.
