You cannot take down a site on a major host from a single computer, as your ISP-limited upload speed WILL be below his speed (being hosted on a commercial line), it would take hundreds of connections or easily more to even put a dent in the site. Furthermore most DDoS attacks are easily detected and blocked by a modern server setup.
DDoSing is trackable and illegal, too. You're not DDoSing him, you're DDoSing the server he's renting, so you're attacking the hosting company, and they don't take that shit.
Don't bother trying.