Be aware that you aren't guaranteed the order will be reliable unless you actually define how the rows should be ordered, using an ORDER BY clause. You're probably getting the rows back in the order they were inserted into the table. There's numerous things that can cause this "default order" to change. It's a really bad idea unless you really understand whats going on under the hood.
Here's an example that sorts the records by firstname. This probably isn't a good column to order the rows by, but we don't know enough about your table schema or requirements to suggest one.
$result = mysql_query("SELECT * FROM `user` order by firstname desc limit 6,1");
print_r(mysql_fetch_assoc($result));