Using wordpress post data as input for google visualisations

Well you can just use the WordPress loop with a custom query to throw all the data you need into arrays.

For example if you want all the post titles in an array (using get_posts);

$all_posts = get_posts('numberposts=-1');
$all_titles = array();
 foreach( $all_posts as $all_post ) {
  $all_titles[] = $all_post->post_title;
 }

As for using the data in Google charts that is up to you, but I would recommend using JSON ( using json_encode), XML or one of the many PHP chart wrappers.