Network Security: How can I protect myself from infected computers in the network?

If a computer has been infected / compromised, there is little you can do to prevent it from attacking other pc's on the network.

Even if you disable services and change network settings, the malware can change it back.

Infected computers are usually on a botnet and send out spam / carry out DDOS attacks. These are difficult to block using system hardening alone. Obviously you need a software firewall and AV to detect and block the malware.

On an uninfected computer with a software firewall you can add the IP address of the infected machines on your network to the "blocked ip addresses list" or similar.

Say you have a network with IP range from 192.168.0.1 to 192.168.0.255
Your gateway is 192.168.0.1 (must NOT be blocked)
Your ip is 192.168.0.2

Hence add 192.168.0.3 - 192.168.0.255 to blocked list in firewall program.