If for some reason, you’d like to exclude some categories from searches, you have to tweak WordPress a bit because there’s no built-in solution to this problem. Happilly, here’s a code to do that job!
To achieve this recipe, replace the categories IDs on line 3 and paste the following code on your search.php template:
<?php if( is_search() ) : $paged = (get_query_var('paged')) ? get_query_var('paged') : 1; query_posts("s=$s&paged=$paged&cat=1,2,3"); endif; ?>
You’re done! See you tomorrow