ZoneAlarm freeware is sufficient for standalone systems that use dial-up or cable/DSL to go online. ZoneAlarm Pro provides flexibility in setup that is needed for some (most?) sytems that are used on networks.
Both work very well and are easy to set up and use. The
ZoneLabs site has online info that will help you determine which you need, and will help you understand the setup procedures for use in special circumstances.
Regards,
Jim