There is a practical side however, and while you can do that using an IOS simulator, its not a substitute for the real thing as you don't haveto plug in real wires, and never experience the joys of configuring an entire network, finding out its not working, and after spending lots of time checking router configs you find out its just a badly wired cable =)
If you can afford it try and find a local center that offers a mixture of in the lab time and distance learning - or even one that just provides access to a lab.