What part of networking are you the most interested in. Are you looking for the TCP/IP side, the network configuration side, there are other ones too. Or are you just starting out and want to learn bits about all of them. I would start by just doing a google search for whatever it is that you are looking to learn about and you will have a huge amount of info at your hands.
Also, I would learn as much as you can about the current network that you are on. Whether it is a small home network with just a modem-router-computer setup, or if you just have your computer connected to the modem and it goes out to the internet. Learn how each of them work, and why they do what they do.
If you have a modem log in to it and look around. DON'T CHANGE ANYTHING UNTIL YOU ARE SURE OF WHAT YOU ARE DOING! Then do a search for things that you aren't sure of and you will learn a lot that way.
The jist of it is that you can do a lot of reading and learn a lot from there.
I think I can recommend the Networking all in one for dummies book here!
Teaches you the basics, gives you a nice foundation and such
I do also recommend prodding around as the last two posts saidm but watch what you do mess around with. You could cause some serious errors but the way I learnt much of what I have so far on networking is through trial and error. Oh and if you want to learn some more, check Wikipedia. Not so good for learning in general, but it rocks when it comes to learning the specifics