ner0 this would probably be better as its own topic, but I am assuming you are running your own IRC server and someone keeps DoS'ing your server. The ways to protect that kind of vary depending on what kind of IRCD you are running (bircd, unrealircd) and the websites for these IRCD's should have information on securing them. There are also service bots that are suposed to protect against this. You can try to go to.

http://194.85.34.34/misc/noflood.html
http://ircd.botbay.net/pub/musircd/musircd-cvs/src/packet.c

Also try searching google.com, and groups.google.com for IRC flood protection.
_________________________
"The secret to creativity is knowing how to hide your sources."
-Albert Einstein

Tech Ninja Security