[progLiker]

Hindsightly I'd start by reading a book about internet security. The only sound thing is to start with a book, giving an overview of the matter and gather information from that point onwards. Most rational thing to do. That's my recommendation.

You wanted to protect your site from attacks: I found a pdf document on the net quite informative: "ethical hacking"(pdf). It covers packet, transport and network layer security up to "google" hacking. It is broken on [http://www.scribd.com], but there are several other similar guides there. And it is out there I found it via google.

There are some good documents at defcon.org as well, I read one about firewalling which was impressive.

You must go elsewhere for cgi security issues, protocols, encryption and all that.