THe first guy's answer is a little over the top, and can be done on the cheap.
Basically to achieve what you need, you need to set up
1. The network. Not really that hard for a home environment. You have a hub and cables, though probably you are going to go with a wireless hub and connect everything wirelessly.
2. Your clients. Windows home is not really designed to work on such a network, and for Linux you might need to install a client, depending on the type of server you are using. Roughly speaking (as there are many releases of windows, all with different versions with different names, you want Windows Professional.
3. The server. Now your school is probably running Windows server, but you can also setup a networking using Linux. The server doens't need to be a dedicated machine, and you could use it as a workstation, but the problem of course is that if you are using it for general use it is more likely to crass. Linux to Windows using requires installing special free software to make your linux system look like a windows server on the network.
4. Configuing it is a pain in the neck. If it works, no problem, but troubleshooting a non working system is painful.
5. Maintaining it. The problem with this setup is that if the network crashes or the server is down, the whole system is down. Meaning, if your little brother wants to surf the internet at 3am and the server is down, he will nag you awake to fish it.
Basically I would recommend a Windows client, linux server solution with a dedicated server.