Um... i know this would sound like a mod (sorry) but i believe that answering that would break the "no discussing on how to hack" rule. Also the tread is probably getting a little off topic. Just saying, and again sorry if i sound like a mod.
Well, to begin with you should take a basic networking class and learn how computers on a network work. Learn the basics such as how a DNS/DHCP/FTP server works. From there you can start to learn more advanced theorys of network, and then try to exploit them.