Most recent post from another database

The WordPress wpdb class is a little different than the normal way of querying in that you run “vanilla” database queries.

You can see documentation on the wpdb class on the WordPress docs: http://codex.wordpress.org/Class_Reference/wpdb#Run_Any_Query_on_the_Database

Also, in regard to your code, you should be able to change the line here:

$originaldb->query_posts( 'posts_per_page=1' );

To something like this:

$results = $originaldb->get_results( "SELECT * FROM $wpdb->posts LIMIT 1" );

This will provide you with an array of posts that you can then process with a loop:

if($results):
  foreach($results as $post): setup_postdata($post); 
    // do stuff with normal wp template tags
  endforeach;
else: 
  // no posts 
endif;