Add quote this to twenty ten header

I’m trying to add Flexi Quotes plugin code to my twenty ten theme header, and replace the site description but I’m getting errors. I don’t know much about php.
This is the code I need to add
<?php if ( function_exists( 'quote_this' ) ) quote_this(); ?>

I’ve been changing

// Add the blog description for the home/front page.
    $site_description = get_bloginfo( 'description', 'display' );
    if ( $site_description && ( is_home() || is_front_page() ) )
        echo " | $site_description";

to

// Add the blog description for the home/front page.
    $site_description = get_bloginfo( 'description', 'display' );
    if ( $site_description && ( is_home() || is_front_page() ) )
        echo $quoteRotator->getQuoteCode();

but I get the error Fatal error: Call to a member function getQuoteCode() on a non-object
Thanks for any help.