I have just upgraded from ZAISS 7.0.483 to ZAISS 8.0.298 without any problems. Didn't even have to uninstall or delete anything, just unchecked "Load ZoneAlarm at startup", re-booted, ensured that Windows Firewall was up-and-running, double-clicked the 8.0.298 installer, chose "upgrade", and re-booted when asked to. Couldn't be easier!
Can report that Scanning Processes are using much less memory than before upgrade.
Operating System:Windows XP Pro
Product Name:ZoneAlarm Internet Security Suite