cant select specific categories using $wpdb->

Hi there,
I am currently using SELECT $wpdb->posts.* to get my pending posts that have a specific meta_key value. but it is not adding my parameter to further sift by a specific category. It works until i add my categories parameter..
my code is below:

$querystr = "
    SELECT $wpdb->posts.*
    FROM $wpdb->posts, $wpdb->postmeta
    WHERE $wpdb->posts.ID = $wpdb->postmeta.post_id
    AND $wpdb->postmeta.meta_key = 'tentativeastatus'
    AND $wpdb->postmeta.meta_value = '" . $tentativeastatusc . "'
    AND $wpdb->posts.post_status = 'pending'
	AND $wpdb->term_taxonomy.taxonomy = 'category'
	AND $wpdb->term_taxonomy.term_id IN(5,18,19,20)
    AND $wpdb->posts.post_type = 'post'
    AND $wpdb->posts.post_date < NOW()
    ORDER BY $wpdb->posts.post_date DESC
 ";
$pageposts = $wpdb->get_results($querystr, OBJECT);

and it functions, until i add my categories ‘AND’

AND $wpdb->term_taxonomy.taxonomy = 'category'
	AND $wpdb->term_taxonomy.term_id IN(5,18,19,20)

remove those two lines, and it functions..
Thanks again,