I tried to install ZoneAlarm Firewall(free edition) on my XP laptop. Unfortunately, it was never meant to be...
First off, my computer took about 5 minutes to boot up. I was like whatever, then I tried to open a program, nothing happened. So I was like this is stupid, and I opened the ZoneAlarm interface. That didn't go well either, I got a "ZoneAlarm detected system instability" message. Then explorer.exe crashed, and didn't come back. I restarted the computer. It booted up normally, but then it started going crazy. Lot of the core processes of Windows crashed, and the System Shutdown in 1 minute thing came up. Apparently svchost.exe crashed. Then I had enough and I rebooted into safe mode and uninstalled ZoneAlarm.
And now my computer works fine again.
The moral of the story: DO NOT USE THIS CRAP!