transaction question

Hello

I have two queries

$result1 = db_query ("INSERT INTO story (value1, value2) VALUES ('%d','%s')", $value1, $value2);
$result2 = db_query("INSERT INTO story_body (value3, value3) VALUES ('%d', '%s')", $value3, $value4);

How I can create a transaction for them. If one query is fail, another is also fail

Thanks
john