which antivirus and how to configure, to protect my lan including all the 8 comps attached to it?

ZoneAlarm Anti-Spyware will work on any LAN connection with firewalls and proxies. Typically, no additional configuration is needed for ZoneAlarm to work on a LAN.
Making your computer visible on your local networkIf you cannot see the other computers on your local network, or they cannot see you, it is possible that ZoneAlarm Anti-Spyware is blocking the NetBIOS traffic necessary for Windows network visibility. To make your computer visible to the others on your local network:
Add the network subnet (or, in a small network, the IP address of each computer with which you're sharing the network) to your Trusted Zone.
Set the Trusted Zone security level to Medium, and the Internet Zone security level to High.
This configuration allows trusted computers to access your shared files, but blocks all other machines from accessing them. Note: ZoneAlarm Anti-Spyware will detect your network automatically and display the New Network alert. You can use the alert itself to add your network subnet to the Trusted Zone. Sharing files and printers across a local networkTo configure ZoneAlarm Anti-Spyware for secure sharing:
Add the network subnet (or, in a small network, the IP address of each computer with which you're sharing the network) to your Trusted Zone.
Set the Trusted Zone security level to Medium. This setting allows trusted computers to access your shared files.
Set Internet Zone security level to High. This setting makes your computer invisible to non-trusted machines.
Note: ZoneAlarm Anti-Spyware will detect your network automatically and display the New Network alert. You can use the alert itself to add your network subnet to the Trusted Zone. Internet Connection Sharing (ICS)If you are using Windows' Internet Connection Sharing (ICS) option, or a third-party connection sharing program, you can protect all of the computers that share the connection from inbound threats by installing ZoneAlarm Anti-Spyware on the "gateway" machine only. However, to receive outbound (Program Control) protection, or to see alerts on the client machines, you must have ZoneAlarm Anti-Spyware installed on each client machine as well. Tip: Before you configure ZoneAlarm Anti-Spyware, use your ICS software to set up the gateway and client relationships . If you use hardware such as a server or router, rather than a host PC, to perform Internet connection sharing, do not follow the steps below. On the ICS gateway machine:
Go to Main tab of the Firewall panel.
Click Advanced.
Under Internet Connection Sharing, select This computer is an ICS gateway.
In the combination box, select or type the IP address of the gateway machine.
Select Suppress alerts locally if forwarded to clients if you do not want to see alerts that are forwarded to a client.
Note: That if you do not install ZoneAlarm Anti-Spyware on the client machines, all alerts will be displayed on the gateway. For best security, make sure the security level for the Internet Zone is set to High. Make sure outgoing DNS and DHCP are allowed for the Internet Zone at High security. On the ICS client machines:
Go to Main tab of the Firewall panel.
Click Advanced.
Under Internet Connection Sharing, select This computer is a client of an ICS gateway running ZA Pro.
In the combination box, select or type the IP address of the gateway machine.
Select Forward alerts from gateway to this computer if you want alerts occurring on the gateway machine to be displayed on this client.

If Connecting through a proxy server

To enable your computer to connect to the Internet through a proxy server, add the proxy to your Trusted Zone

But if you want all three in one then use ZoneAlarm Internet Security Suite, which integrates anti-virus, anti-spyware and a firewall.