Excluding categories from a random post plugin

Hey, what I want to do is basically do what this following plugin does, but exclude my NEWS category – and in the future possibly more categories.

Here is the plugin, thanks in advance:

<?php
/*
Plugin Name: Random Posts
Plugin URI: http://www.w-a-s-a-b-i.com/archives/2004/05/27/wordpress-random-posts-plugin/
Description: Displays a configurable list of random posts. Usage: random_posts();
Version: 1.1
Author: Alexander Malov
Author URI: http://www.w-a-s-a-b-i.com/
*/

function random_posts ($limit, $len, $before_title = '

• ', $after_title = '

', $before_post = '', $after_post = '', $show_pass_post = false, $show_excerpt = false) {
global $wpdb, $tableposts;
$sql = "SELECT ID, post_title, post_content FROM $tableposts WHERE post_status = 'publish' ";
if(!$show_pass_post) $sql .= "AND post_password ='' ";
$sql .= "ORDER BY RAND() LIMIT $limit";
$posts = $wpdb->get_results($sql);
$output = '';
foreach ($posts as $post) {
$post_title = stripslashes($post->post_title);
$post_title = str_replace('"', '', $post_title);
$permalink = get_permalink($post->ID);
$post_content = strip_tags($post->post_content);
$post_content = stripslashes($post_content);
$output .= $before_title . '' . $post_title . '' . $after_title;
if($show_excerpt) {
$words=split(" ",$post_content);
$post_strip = join(" ",array_slice($words,0,$len));
$output .= $before_post . $post_strip . $after_post;
}

}
echo $output;
}
?>