The built-in Windows firewall is very good in Vista and Windows 7. The firewall in XP could be very good as well if it was configured properly. If you are using good antivirus like Trend, you don't need to purchase another firewall product. A lot of people think you need to buy the "internet security" suite product made by the antivirus vendors.

We don't care for those tools as they tend to be more trouble than they are worth. The settings are difficult to control and the products are often overly-aggressive.

If you are a home user with a very basic environment, then the internet security suite might be good for you. But everyone else who requires their computers to talk to each other needs to be able to control those communications and the internet security suites conflict with those purposes.