Zone Alarm free/pro/suite all work fine on Win98 (SE) and seems to be fine on Win ME, but 2000 and Xp seem to have problems with it, but i am using Sygate at the moment on my Win98SE and it seems fine.
I have never used Ouypost so i don't no about that.
I tryed Kerio before (i think it was beta version) and it blocked everything from the start bar to my Documents, i couldn't even access my drive though My computer, and get this, it did some alert haker thing when i tryed to restart my comp, i had to start my computer in safe mode and manuly remove it.
--lee