How to Become a Network Administrator

Clarifications

http://www.cbtplanet.com/network-administrator.htm

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If you want to hit it from the software side, I'd recommend getting a trial version of Server 2008 and playing with it at home on a junk computer.

On the hardware side, the de-facto name in Network Administration is Cisco. I'd recommend getting CCNA certified and maybe a Network+ from CompTIA on the side. The CCNA is far more impressive on a resume, but it tends to forget that you're going to be working on computers as well as network hardware. The Network+ brings the computers (PC's, Mac's, and *nixes) back into the networking equation.

Further more, I recommend you do a little hacking of your own network.
http://www.tech-faq.com/packet-sniffer.shtml
Packet sniffers tell you what's going on and what's being passed. They're a handy tool to help you keep an eye on what's getting passed.

On a further note, I had a co-worker in my last company who routed the 100+ employee network through Linux servers. I'm currently dabbling in the dark art of "ip route" with astonishing findings.

This may sound like a lot, and it is, but you should already understand by now that what they teach in college is only the tip of the iceberg and the real skills you need can only be earned and learned through personal experience.