I love the comments about the brain surgeon.

However, there are many books to look at if you're interested in network security.

There are many facets to it as well. Are you interested in general firewall type security? Do you want to be router/switch specific? Or are you interested at the OS level? Itrusion detection? forensics?

I would start out by getting some books on the specific topics you are interested in starting out in. Personally, I would begin with what you have close to you now, maybe Windows? SANS has some great online courses.

Good luck...