Limit Amount of Pages users can create in Custom Post Types

Check out my plugin Bainternet Posts Creation Limits
this plugin helps you to limit the number of posts/pages/custom post types each user can create on your site.
Its just what you need.

Update

open up bapl.php and in bapl_limit_post_count function change on line 44:

if ( current_user_can('manage_options') ) {}else{ 
            if (isset($postt[$curent_type])){
                //$postt= bapl_getOptions('bapl');
                foreach ($postt as $key => $option){
                    if ($key = $curent_type) {
                        $ptname = $key;
                        $limit = $option;
                        break;
                    }
                }
                //print_r($postt);
                $count_posts = count(get_posts(array('author'=>$current_user->ID,'post_type',$ptname)));

                if ($count_posts >= $limit){
                    //wp_die( __('You Can\'t Create any more pages of this type.') );
                    bapl_not_allowed();
                    exit;
                }
            }
        }

to:

        if (isset($postt[$curent_type])){
            foreach ($postt as $key => $option){
                if ($key = $curent_type) {
                    $ptname = $key;
                    $limit = $option;
                    break;
                }
            }
            $count_posts = count(get_posts(array('author'=>$current_user->ID,'post_type',$ptname)));

            if ($count_posts >= $limit){

                bapl_not_allowed();
                exit;
            }
        }

this way the admin is limited too.

Next you will need to change bapl_getOptions function and set you defaults there.
And last you will probably wont to remove the admin control panel of this plugin so comment out line 69 were it says :

add_action('admin_menu', 'bapl_menu');