If you hear a person proclaim that all computers need a firewall, then ask "Why?"
For instance, Windows 95, 98 and ME with the last updates and not sharing a file system are not exploitable. That is, there is no known way for a remote user to do harm to the machine. In the case of Windows NT, 2000, XP and for now the next OS's from Microsoft, simply using the TCP/IP security will stop exploitations, but those tend to be hard on the users since some learning is involved.
For XP, Zonealarm is ok for the default settings, but beware that using such without understanding often results in complaints that "the internet isn't working."
Can anybody recommend a Free Fire Wall thats free and does the job