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
Oh and you could check out wikibooks/this link
Sorry if I was of no help, I'm just trying my best to help out as well as I can
Sorry if I was no help :S I'm just pretty new to helping other people with tech problems lol