-> Network different computers with different OSs in your room, get everything to play well together. Challenging, edumacational, and when its works its quite satisfying (I'm working on it myself nowadays). If you have space, throw in a big wooden table to spill your computers' guts out, since you are interested in hardware, as I am. (There is a definite hardware angle to system security, part of protocol ya know.)

-> Take the certifications, if you want to, later on, after you have the hands on. If you really want to, you can find the certs out there and try your hand, since they are usually randomized tests, take them as many times as you want. But remember, the certs mean **** if you can't do it hands on.

-> You can network your boxes through a switch, but try other configurations as well. Each new set-up will give an array of challenges. Whatever form of linux you put on, you might try using a linux box as the gateway/firewall, (configure IPchains/tables) and I think that will help your TCP/IP know-how quite a bit.

-> always always read the forum.

-> Read the book "Security Engineering" by Ross Anderson, for a panoramic view of security.