Here's what I use...

I use the free version of Avast and Comodo firewall also free. These haven't caused any issues with me. they work well together and Avast will defer to Comodo or allow it to be the firewall. However, Win7 own firewall is quite sufficient to work if you find it doesn't take any other firewall. Avast can then assume or continue to work well on its own merits. I offer the above if ZA proves to be problematic.

tada ------Willy happy