is an excellent website for this sort of thing. Once you've got the basics covered, I'd recommend listening to some of the Security Now
episodes on computer architecture - very good explanations on this kind of thing! I'm not going to list the episodes you should check out, because there are way too many essential ones. But basically, start at the beginning (scroll to the bottom of that page and pick the oldest year) and if I remember correctly there are some early ones on NAT, wireless, ethernet and such which offer very clear and detailed explanations (text transcripts are available at that site too, and video from http://twit.tv/sn
if you prefer a visual medium rather than audio.
Enjoy your learning, I hope you get what you want out of it.