While these will work, you'll lose the ability to use the "other" custom features such as get_post_custom and wordpress queries. The simple solution is

$wpdb->select('database_name');

which changes the database system-wide (a mysql select_db). The database.table method works if you just want to make a simple query, but if you want to access another wordpress blog you can use select. You'll just need to change it back when you're done or your blog may do strange things.