Okay. that takes a little more effort.
first off you'll need to gain controll of many computers.
like... a thousand or so.
you can do that by spreading a backdoor virus through a school network, or a mass e-mail that says 'free money! click here!'
from there, you force all thoes comptuers to 'ping' a specific domain at the same time.
computers are very fast, but with a thousand systems each sending a thousand requests every minute, it compounds quite quickly, and then the service can't respond to anything. (it dosn't know what to ignore, and what to respond to)
if you can keep thoes thousand systems up and running, you'll probibly be able to deny service for about a week or so before they block the domain it's coming from.
if you have it on a widely spreading virus, then they'll be fighting with it for years to come, and probibly end up having to change their domain name.
there are a variety of packages you can put it into.
http://astalavista.box.sk/you mostly have to write your own code for it though. most virus software already protects aghinst the currently mass-email applications you could get access to easliy.
(although with only a little programing knowhow, you could edit them enough to make them your own)
-RuskiFace the Pirate