I ran into this issue a while ago where I lost internet access connection after installing a windows update and turns out to be because of my ZoneAlarm installation. [more]
Update KB951748 is known to cause loss of internet access for ZoneAlarm
users on Windows XP/2000. Windows Vista users are not affected.
Sudden loss of internet access
Platforms Affected :
ZoneAlarm Free, ZoneAlarm Pro, ZoneAlarm AntiVirus, ZoneAlarm Anti-Spyware, and ZoneAlarm Security Suite
1) Download and Install latest version
2) ZoneAlarm Firewall Internet Zone to medium
3) Uninstall the windows update
Read the full article from here posted July 8, 2008
There are also mention in the forums about uninstalling and reinstalling but also a mention that it does expose some vulnerability in which the update was intended for.