I have used PC Guard (and its predeccesoor with ntl, whatever that was called) for years and have always been happy with it . . . until this latest Kapersky version. On both my old XP laptop and my powerful Vista desktop, there have been many problems, particularly incredibly slow to turn on. Something to do with it also tried to prevent them from shutting down from time to time.
I have uninstalled PC Guard and Broadband Advisor and installed the new Microsoft one. Only been on for a week but so far I am impressed. The reviews are encouraging. It is free. I find Windows firewall (plus router firewall) quite adequate
Find it here