If you want to be a Dr. you don't start cutting up people before you know ANYTHING about anatomy. I think that you should either purchase at a bookstore, or go to
http://safari.oreilly.com/ (nothing to do with the mac browser) and read the following (at minimum):
TCP/IP Network Administration
Practical Unix & Internet Security (crucial)
DNS and BIND (optional)
There are others you could also read:
Ethernet: The Definitive Guide
IP Routing
IP v6 Essentials
Network Troubleshooting Tools
If this is for a class, then you need to check out the prerequisites. Something is missing. Not trying to dis you at all, mind you. There is nothing wrong with wanting to learn about networking and security. White hat hackers are cool. In Europe, there is a group that probes different network services, like ldap, snmp, imap, and hammer them until the find all sorts of unknown bugs. This forces development of better versions of code. Just last year, they found something like 26,000 messages you could send to an snmp server, that could crash a system. SUN, Cisco, Foundry, all the players were forced to come up with new software to protect the services. I think that is great.
If you start blindly hacking away, you will not learn much. Become friends with O'Reilly books, they really jumpstarted my knowledge and set me on my path into my current job.