You have to alias the postmeta table for the second value:

	$querystr = "  
            SELECT $wpdb->posts.* 
            FROM $wpdb->posts, $wpdb->postmeta, $wpdb->postmeta AS mt1
            WHERE $wpdb->posts.ID = $wpdb->postmeta.post_id 

            AND $wpdb->postmeta.meta_key = 'key1'   
            AND $wpdb->postmeta.meta_value = 'value1'
            AND mt1.meta_key = 'key1'
	        AND mt1.meta_value = 'value2'

            AND $wpdb->posts.post_status = 'publish' 
            AND $wpdb->posts.post_type = 'post'
            ORDER BY $wpdb->posts.post_date DESC
                ";

You can also do this now since 3.1 with a [`meta_query`](http://codex.wordpress.org/Class_Reference/WP_Query#Custom_Field_Parameters):

	$args = array(
		'meta_query' => array(
			array(
				'key' => 'key1',
				'value' => 'value1',
				'compare' => '='
			),
			array(
				'key' => 'key1',
				'value' => 'value2',
				'compare' => '='
			)
		)
	);
	$query = new WP_Query( $args );