before start

Before start.

need Pecl Mongo

you need to install Pecl Mongo.
http://pecl.php.net/package/mongo

If you have some problems, please see follow URL.It’s good information for you.
http://www.mongodb.org/display/DOCS/Installing+the+PHP+Driver

database.php

class DATABASE_CONFIG {
    var $default = array(
        'datasource' => 'mongodb',
        'host' => 'localhost',
        'login' => '',
        'password' => '',
        'database' => 'blog',
        'port' => 27017,
        'prefix' => '',
    );
}

Sample files

some sample code in repository.
It needs to set some properties in each mode. Please see sample post model.