I had problems with my XP SP2. It was running badly and hang a lot, even when I opened Notepad, my computer froze and the internet connections went down to zero.
I have been looking all over the net for a reason and a solution and when I read this I uninstalled my ZoneLabs (ZoneAlarm) 5.x and everything is running great now.
No Lag, No Hanging, P2P programs running fine......so far :)