In my home I have two linux box and 1 windows, I want to setup linux as a sever and other 2 as a clients , how can i set it up?

Basically, you will need a network. Every computer will need a network adapter. It might be built in some of the computers already or you might have to buy it separately.
You will also need network cables. Buy some in a store near by. Chek your furniture/room set up and estimate lengths of tha cables to buy.
Then you will need a switch. It is a small device with several ports for plugging in the network cables and it will allow the computers to be able to talk to each other.
Of course, you will have to install networking to all the computers' operating systems and set it up properly.

I have all that, I want to setup networking inside machine ...HOW?

When you say you want to set up your computers as a network that encompasses many different possible services. You can set up your server to perform windows-like network services via Samba. You can set up a DHCP service to pump out ip addresses and other information to the computers at boot up. You could set up a web, email, or ftp server in combination with a DNS server for for an internal network. You could use one computer to share internet access and provide firewalling. You could set up NFS sharing for file sharing only between your linux boxes... theres tons of possibilities. As far as the how, your best bet is to start reading howtos, man pages, and visiting web sights that provide these open source services. Your distro might have already installed these capabilities on your system. Look for programs like Samba (windows stuff), Bind (nameserver stuff), Apache (web stuff), DHCPD (dhcp stuff) etc. Reading forums in the networking area can also provide ideas as to what other people use for these things. You also want to make sure anything you set up is protected from unwanted visitors.