ZoneAlarm Extreme Security Suite - Ver.
No other Security software other than Windows'
Windows Vista 64bit Home Premium
HP Desktop - a6750f
came with Norton Inter. Security pre-installed, starting about 2-weeks ago:
Uninstalled Norton via "Norton Removal Tool", then within 3-days:
Installed/Uninstalled Z/A Free Firewall and AVG Anti-Virus Free Edition 2011;
Installed/Uninstalled (clean) Z/A Internet Security Suite
Currently Installed - Z/A Extreme Security Suite

How are you suppose to configure Z/A firewall to "allow UPnP discovery"?. That is part of the error message I keep getting when I have tried to connect my Xbox 360 to my Desktop's Window Media Center as an "Extender" (and the Xbox wouldn't list my computer either). While using the Norton I had no issues the problem started after uninstalling the Norton.