Querying two taxonomies

This helper function will return the ID of the term you are currently viewing (from any taxonomy – you can limit just to a specific taxonomy, or the built-in tag and category taxonomies).

It will return false if you are not on a taxonomy term archive page.

function wpse52578_get_current_term_id(){
    if( !is_tax() && !is_tag() && !is_category() )
       return false;

    //If we got this far we are on a taxonomy-term page
    // (or a tag-term or category-term page)
    $taxonomy = get_query_var( 'taxonomy' );
    $queried_object = get_queried_object();
    $term_id =  (int) $queried_object->term_id;

    return $term_id;
}

Then you can do something like the following:

$tool_term_id = wpse52578_get_current_term_id();
$tax_query = array( 
             'relation' => 'AND', 
             array(
                'taxonomy' => 'guide-type',
                'field' => 'slug',
                'terms' => 'video'
            ));

if( $tool_term_id ){
     $tax_query[] =  array(
                'taxonomy' => 'tool',
                'field' => 'id',
                'terms' => $tool_term_id
                )
 }

$args = array('tax_query' => $tax_query);
$query = new WP_Query( $args );

Note: I’ve not tested this