Same issue - I uninstalled Zone alarm free version 9, switched on Windows firewall, everything now smooth. I have seen a fix posted elsewhere for Firefox users, open up all servers in Zonealarm program permissions - Internet & Trusted.

This has worked on another machine of mine with AVG and Zonealarm (same versions) running OK - but it never had the same degree of problem. Do the same for other services you trust and it seems to fix them too, but still runs a bit slower than taking out Zone Alarm completely.

Hope this helps someone! I will look at other firewalls now.