title says it all…
windows vista.
I’ve used both Comodo Firewall and ZoneAlarm’s free firewall in the past; both are decent.
(Note: ZoneAlarm’s site makes it tricky to find the actual download for their free firewall without being bombarded with offers to “upgrade” or to get a trial version of their not-so-free software. Here’s the direct link to the ZoneAlarm free download on CNet.)
Best Free Firewalls with detailed reviews
Best free everything for Windows:
Why not the one built into Vista?
Run far and run fast from ZoneAlarm, it is probably one of the least effective FW/AV suites known to man. And then when you find out just how bad it is… it will be nearly impossible for you to wipe it from your system without a manual search of your drives and registry.