Hullu!
Do you need a software-base firewall that you can configure to allow certain programs from accessing the network? In which case, I would suggest this product as your open source, free alternative.
http://www.ghostsecurity.com/ghostwall/If your looking for something with a more comprehensive suite such as virus and malware protection with a built in firewall, I would suggest this product.
http://www.sunbeltsoftware.com/Home-Home-Office/VIPRE-Antivirus-Premium/Hopefully this answers your question, ^_^!
