jQuery breaking my wordpress site

You should not include jQuery manually. jQuery is included in WordPress by default, but isn’t loaded on every page unless a plugin or theme requests it. This can be done using:

add_action('wp_enqueue_scripts','my_scripts');
function my_scripts() {
    wp_enqueue_script('jquery');
}

Here is function reference for wp_enqueue_script (the function) and wp_enqueue_scripts (the action hook).

In addition to that, WordPress is using jQuery in no-conflict mode. This means you cannot use the normal $() function, but have to use jQuery() instead. For example, instead of this:

$('selector').doSomething();

Use this:

jQuery('selector').doSomething();