WordPress doesn't use a Google CDN version of jQuery; rather, it bundles a version of jQuery (currently, version 1.6.1) in core.
To use jQuery on the front end (i.e. in your Theme), you need to add something like the following to functions.php:
function mytheme_enqueue_scripts() {
if ( ! is_admin() ) {
wp_enqueue_script( 'jquery' );
}
}
add_action( 'wp_enqueue_scripts', 'mytheme_enqueue_scripts' );
If you can provide a bit more specific information about what you're trying to do, we can provide more specific assistance.