Norton is compatible, provided you have the latest version installed. McAfee, Computer Associates, ZoneAlarm, Kaspersky, and others are also Vista-compatible. However, if you would prefer a free option you can click here for a list of the top contenders. I have not updated the list yet, but ZoneAlarm has also released the new version of their free firewall, which can be downloaded by clicking here.

Hope this helps,
John