Could you get yourself some cheap pcs, a hub and some cables to play around with.
The internet could teach you a lot for free.
I'm by no means a networking professional, but when I wanted to learn home networking I used Samba on Linux as a project.
The objective was to set up a Linux Samba machine which 2 x MS Window machine could see and use the file share on.
If you have a broadband router, you can start playing around with that. Set up DHCP server and dish your PCs out a different Address Class. Just little things. Break your network, fix it, try and improve it.