I don't think the Vista firewall is up to much (although better than XP!) so I have ZoneAlarm, for virus I have Avast (also free & excellent) and for Spyware I've ditched my old XP stalwarts of SpyBot & Spyware Blaster and now run: Threatfire(free), Spy Sweeper(paid for updates) and Defender. NO conflicts with extra Spyware programs at all, and as has been said some find things that others don't.

Only other thing I would add is once the subscription has ended (and watch they don't renew it without asking!!) scrub it and go to the excellent range of equally good, possibly better, certainly less bloated on your system, free ones