Use Google. Preface your search with 

site:matrixgames.com 

and include 

+"War in the Pacific: Admiral's Edition" 

or whatever sub-forum you want to search.

To search just the Tech Support sub-forum make sure to include this: 
+"War in the Pacific: Admiral's Edition >> Tech Support" 

So if you wanted to find posts in Tech Support with the word "crash" in them, Google this: 

site:matrixgames.com +"War in the Pacific: Admiral's Edition >> Tech Support" crash 

Don't bother with the built-in search. Using Google works better. Hope this helps.