Bit of an old post, but I think that there are enough people with the same problem, so I'll just post the solution.
You must know that this behaviour is on purpose. But the solution is quite simple. Put the following code into a file named
dontsearchpages.php, upload it to your plugins directory and activate it on the Plugins page of your blog.
Plugin Name: Don't search pages
Plugin URI: http://lxg.de
Description: Disable searching of pages.
Author: Alex Günsche
Author URI: http://lxg.de
$query = str_replace
("AND wp_posts.post_type != 'revision'",
"AND wp_posts.post_type != 'revision' AND wp_posts.post_type != 'page'",
Tested with WP 2.9.1 – may not work with earlier or later versions, as this is quite a dirty hack.
Inspired by an early WordPress plugin called Search Pages – which did the opposite of this one, back when WordPress didn't search posts. :)