I use Online Armor Free. Very light on the PCs resources. And one thing that I really like about Online Armor, it has a new version every now and then (in my experience, almost every 3-4 weeks). Meaning it has updates for the firewall. Works with Vista (32) and Windows 7 (32). In the set up though, you need to allow the components of Avast, and for the Firewall to TRUST Avast. It would be smooth sailing after that. Well... At least in my case.
One good reason why not to use Comodo: It made my PC freeze after Avast updated itself. And take note, Avast is in Comodo's Trusted Programs. I ditched it after that. Uses a lot of memory and CPU power also.
Mikos