First off, I'm assuming we are talking about ethernet and not anything else. Personally, when I first started to get into networking a few years back I spent alot of time at this site

http://www.ethermanage.com/ethernet/ethernet.html

It is by a guy that works for the University of Texas in Austin named Charles Spurgeon. These guys have been at it for a long time and they pretty much know their stuff.

Charles Spurgeon also has a book published by O'Reilly called Ethernet: The Definitive Guide

Its not too bad on the pocketbook and it really breaks it down.

Ethernet and TCP/IP are great places to get your feet wet but if you ever get bored with it, which I can't imagine how one could, and you want to get into WANs, which, personally, I love, try starting here
http://www.cisco.com/univercd/cc/td/...c/introwan.htm

It's a pretty straight forward starting point. And feel free to ask me anything anytime. Because of the environment I work in I get a chance to mess with alot of stuff most people in the private sector and/or industry don't get to mess with. That can be both a good thing or a bad thing sometimes.

read on,
nocilis